We agree that needs to be improved but here is the catch:
Because the actual real world coastlines have infinite length and because even a rough estimation is in the millions of km this means even at rough 100m intervals we are talking about >16 million points. Even if someone would be able to manually create one point every second this would be a 24/7 task for 185 days straight without sleeping or in realistic terms 2.1 years without vacations.
So masking the water manually for the entire world is out of the question.
This leaves us with automatic solutions but as you can imagine we also do other things besides just water masks. We have looked into coastlines from OSM but they are also inconsistent at times which means the algorithm would need to handle a lot of edge cases and invalid data such as coastlines removing the land instead of the water, etc. So this requires more work that we thought and we paused it for now. We plan on continuing this at some point in the future.
Also even in areas with really bad coastlines in msfs, the water structure makes it look natural, the water in msfs isn't just a coloured surface and it does have a consistency and the coast lines look super natural