I think your two issues are more related than you realize. So while my goal is to answer them both, I'll be interweaving my answers across multiple points instead of tackling them separately. And I'll be doing so with a single (longwinded) analogy:
Let's say you've never golfed before and decided to pick up the sport. You also want to golf a few times a week. Many golf courses, if you don't know, won't let you "golf alone" unless they are very slow. A single player is a spot on the golf course that doesn't make them as much money as a group of four does. And is also usually a sign if a player who might have issues that slows down play for groups behind them.
Now for a small tangent: Many golf courses won't turn away single players. But they forcibly pair them up. It is not uncommon to show up as a single and be asked to wait until a two-some or three-some (or multiple other singles) are also waiting, and a tee-time opens up (cancellations, etc). And if you call ahead for a tee-time, they'll either pair you or keep a list and call back if they get other requests that they can pair you with.
So if you, as a new golfer, might want to play and might not want to get paired with randoms. So you want to meet some folks an establish a regular group to golf with. Completely reasonable. How would you go about all of this Well, for starters, almost nobody can teach themselves how to golf. You need someone to teach you. Sometimes that can be a peer, but in the golf world, it is very common to pay for lessons from a professional. They get paid to be patient and help you. But believe me, if you mouth off to your new coach, they'll likely decide your money isn't worth it and walk away.
Let's apply this to Sea of Thieves. There are no paid coaches that I'm aware of (and might be against terms of services if there were) but there are plenty of good pirates out there willing to lend a hand. But like golf, trying to learn while playing solo will not teach you much (usually.) You are just too busy multitasking to get any good practice at any one thing, and that means you don't learn at the pace you probably want or need to.
Which means you have to go into finding a crew with HUMILITY. From your post, I can interpret that you have not been patient with some crew members in the past, and getting removed from discord is another red flag of some behavior that you probably have to look inwards at changing. Nobody wants to golf with the person who throws their 5-iron in the pond because they landed a shot in the sand. Know what you don't know and be willing to learn from the folks who want to teach you (because it benefits them!) That goes a long way to both getting a crew, k keeping a crew, and learning more about PvP.
Next thing. Once you know the basics of golf, you still have to practice. You don't practice golf by going out on the hardest golf course you can find and accidentally putting yourself in the most troublesome places your new (still learning) skills happen to land you in. No. Golfers, new and experienced alike, use this place called a "driving range" to practice. They hit an entire bucket of balls using one club (or two, or maybe three.) Sheer repetition so your brain and your muscles connect. So you learn that "on average" your 5-iron goes 150 yards for your muscle strength, bone density, height, etc. And you start making small changes to your swing to correct that rightward drift that seems to happen in every shot you take. Sure, you still go play golf sometimes, and hopefully have a group of folks you now golf with (maybe you got paired with them as a single one time.) But you also practice. A lot. Because that is how you learn and improve.
In sea of thieves, that means playing with your group and taking on a specific role. Again, if this is the group also taking on the challenge of teaching you, listen to them and take the role they ask, not necessarily the role you want. Good bilgers didn't just get there overnight. They spent plenty of fights just bucketing out of a grate and seeing water splash in their face to get the muscle memory to see the rock of the ship, the angle they need to throw, the pace at which the animation resets. It takes a lot of practice. Same with helm. Same with cannons. Same with boarding. You can't do it all at once. Many crews do rotate out to keep their skills sharp (enough) but will also learn who is good at close quarter vs sniping across the waves vs anticipating angles to lob cannonballs. I've known very experienced pirates who can hit a snipe shot on someone on an opposing wheel at distances that you'd think might be cheating. But cannons were so potato that they rarely got on cannons in a heated PvP fight. (which also leads to accusations of aimbots, but we play on xbox, and I know this dude in person, he doesn't aimbot.) So in PvE, we swap things up and do whatever needs to be done. But in PvP, he will bilge and snipe as opportunity allows.
As you practice, you'll learn your strengths and weaknesses. Don't be demanding of your crew; they know your strengths and weaknesses to and chances are they will ask you to do whatever gives the crew the best chance to win. If you are consistently going against that grain (leaving ship to board and then getting blackscreened when taking a mermaid because inevitably you missed, and then the ship sinks because they were short manned....well....chances are you'll stop getting invites to crew up with those folks even when they see you online.
Which brings me to the PvE to learn PvP. Again, like a golf course, when playing a real round, you'll find yourself in all sorts of situations that the driving range and practice green will never put you in. You'll be in sand. OR land on a sprinkler head. Or behind a tree. And you'll have to improvise to get yourself out and your score will probably suffer for it. But that doesn't mean the practice wasn't worth it. PvE will still help you better judge range on cannons. Or learn how to bail when those ghost ships put 25 holes in you. You say you are either too far or get tanked....which is exactly the kind of practice you need (maybe not solo!) but multitasking, communicating with the crew, and prioritizing. How far can you push letting the water rise to eliminate ONE MORE ghost ship before its all hands to bail? How fast can you recover so you can deal with the next wave? None of this changes with PvE vs PvP. The only thing PvP does is throw more at you. PvE will aimbot your ship, but good PvPers know when you are on cannons and might harpoon you. Or know when you are on ropes to recover your mast and will aim at that section of the ship....decisions PvE AI's don't make. Take the multitasking balancing act of PvE and turn it up to 11 because you have to learn when to disengage from the ropes and eat. Or deal with suddenly being harpooned onto another ship (pro tip, they are still on harpoon and you are dropped behind them. Fast reflexes and a blunderbuss can turn their good play into your better play pretty quickly.)
The point being that PvE still gives you the fundamentals like a driving range does, and then PvP throws a bunch of unexpected stuff at you (because players are erratic, where AI is not) like a real golf course would. PvE forces you to multitask and prioritize. PvP adds an element of needing to improvise on top of it.
But 100% first and foremost, you need a crew. And you need to be patient with them because I absolutely promise you that, based on your question, they are being more than patient with you. LFG is still a fine way to build your friends list to sail with (don't solo!) and spread it around until you find that person or group you really click with. They'll feel the same most likely (its like dating...when you know, you know.) But if you go out on a date and wear your grubbiest t-shirt and belch and yell at the waiter that your soup was cold, chances are you aren't getting a second date with that person. And, like dating, don't be needy. Its okay to play the field. Crew up with different people if they are online. Have a friends list that is 20-40 people deep so there is always someone online interested in playing. Take what comes to you instead of demanding someone play with you because you are ready to play.
Eventually, you find that person/crew who happens to keep a similar schedule and has complementary skills. And then you sloop it up. Or decide to try to build out more towards a brig. Or a galleon. Or you find you got invited to a brig/galleon from LFG and its a crew that works ...ready-made! If you are patient and not a jerk to them. ....but let's not go down the rabbit hole of having a regular 3-some or 4-some date. That could get awkward. Unless you are Bill and Ted and married some medieval princesses. (Bonus points for those that got the reference.)
Carry on. That's just one man's lame advice.
