In potbs number of sailors where huge, on big ships you where literally seeing hundred, but there was an option for show less between 10% and 100% and also at what distance but more important you where seeing them going up and down mast, repairing etc (also much more variety, we have pretty much sailors all dressed the same, and you cant see different kind of sailors example marine infantry etc would be cool see lobsters on hms ships etc )
fps like, they are pre calculated 3d object with a fix animation, the number of polygons is very low, they can put literally hundreds first than have a problem, a 50 ship battle probably will have a 5 fps drop at top expecial considering you not display/load them at a certain distance (at moment quite low)
See? much more alive is the only part where potbs is superior to naval imho, the feeling of have an "alive" ship the rest is too arcade..