One of the biggest complaints I see people making about this game right now is that all the quests (or "voyages") are the same. Quest giver tells you to go find something on another island, you go get it, and you bring it back to them at the outpost (usually without having to travel very far). They're intended to be a starting point for the players to make their own adventures, which is fine, but I do believe there's some room for a little more variety in these starting points.
Looking at this post on MMORPG.com, there are essentially 10 different types of quests in MMOs:
1. Kill X of Y - Defeat a certain number of one type of bad guy.
2. Kill Named Y - Defeat one particularly powerful bad guy
3. Delivery - Take something from the quest giver and deliver it somewhere else
4. Collect X of Y - Find a certain number of some kind of object
5. Escort - Lead an NPC from point A to point B
6. Locate - Either a "go find the place/person/item" quest, or just a "go to this place/person/item" quest
7. Defend - Defend someone or something as waves of attackers try to kill it
8. Interact - A variation on Locate where you have to activate something at the location(s) you're going to
9. Crafting - in games with a crafting system, quests that encourage making stuff with it
10. Reach Achievement X - level barrier quests that keep you from advancing too far into the story when you're not strong enough
Looking at this list, it's easy to see why Sea of Thieves might feel a little stale on the quest front. Generally speaking, there isn't a lot of variety to be had in MMOs to begin with, and Sea of Thieves is a very unusual sort of MMO, deliberately designed with horizontal progression and no story. So some of these quest types simply won't work here. 9 & 10 are definitely out, but that's okay, because they're filler quests, anyway. Let's look at what we have and what there might be room for.
-Quest types 6, Locate, and 4, Collect, are probably the only ones we can definitively check off as implemented. There are elements of Escort and Delivery inherent in these quests, as well, but in an unusual form, where the only potential obstacles are other players.
-Quest types 1 & 2 seem likely to be covered, to a certain extent, by The Order of Souls. We'll likely need to hunt down a certain skeleton to take his skull back to the quest giver.
So where is there room for more?
-The easiest to implement, and most suggested I'm seeing, is Delivery. Instead of playing fetch for the quest giver, play mailman. Take something he gives you (perhaps something you just brought him from a previous quest?) and deliver it to a different outpost.
-Escort is a possibility, but would require the addition of perhaps NPC ships. Maybe the quest giver doesn't trust us with his cargo, but needs some hired guns/cannons to keep him safe from other players.
-Kill quests (1 & 2) may already be covered to an extent, but maybe there's room for some headhunting quests. Some player p****s off one of the Gold Hoarders by stealing a chest that was supposed to be delivered to them and taking it to a different one or something, so now they've got a price on their head.
-Defend is possibly sorta-kinda in place with the skeleton forts, but it's more attack than defend, at least until you get in there and take the loot, and then the defense comes in the form of PvP. Adding quests of this type while maintaining the loose, player-driven non-narrative lore might be difficult.
I guess what I'm trying to show with this is that while, yes, the quests we have currently are repetitive, and yes, there's a little bit of room for variety, MMOs don't have a whole lot of it to begin with. And when you're deliberately trying to give the players control of the story, you're even more limited. So maybe the playerbase should be thinking of this game less like an MMO and more like a Battle Royale, I don't know. Find your fun outside of the quests, is my point, I think. And hopefully Rare will add some degree of variety to those quests later on.
