I'll give your idea credit. It's fun, doesn't change any real game mechanics, and gives people who have worked toward something a certain "reward". It's for sure interesting and immaginitive.
I have a few problems, however. One is, what constitutes a "win/loss" ratio? # sinks/# times sunk? Is this only for player ships or do ghost/skelly ships count as well? I think you'll find that because of the numerous activities pirates can take on the seas, this number will probably poorly reflect any actual "danger" a certain player presents. This is not a combat game. It's an adventure game with pvp elements. That makes any statistics very difficult to measure how "good" or "dangerous" or "skilled" a player is. Ship size, under-crewed ships, regular crew vs open crew, etc are just a few of the variables that would be so mind-boggling to calculate into anything meaningful that the end result will be not worth the time/effort/coding to implement.
Secondly, I feel like, unless this is optional or could be toggled, it might take away player agency. Say I'm a very skilled pirate with many sinks under my belt. I might be considered "deadly" according to whatever metrics the game uses. But what if I just want to sail around and make friends? If I could not toggle this setting off, then many and most players will not trust or want to interact with me because of my "deadly" status. If you can toggle it off, then it becomes more of a "cosmetic", which I have no problem with, but also becomes useless in "altert[ing] lower skilled players".
Another thing to consider is that maybe I'm a super great deadly player, however I'm playing open crew with people who are new, or maybe I'm hopping on for a nice fishing session with my daughter or something. People on the lookout for good fights might track me down and attempt to engage when I'm really just not looking for that. I know that might happen anyway, but in those situations I do what I can to not paint a target on my back, and this paints a target on my back.
I think it's a fun, creative, cool idea. I just don't particularly enjoy what it would do to the game. I feel like with Streamers normally showing combat against other players, it has given certain communities the idea that that is what this game is! PVP fighting other pirates. And that is certainly a part of the game. But there is far more to it than that, and my most fond memories of this game have been times when I've had fun with my crew, formed great alliances, and just tried to enjoy my time without worrying about my K/D ratio.