Yes, this is true. Currently the cheaper shiping causes massive spamming of fleets, expecially with the Byzantine. This makes no sense as they are not set up in the startpos file as a trading faction. When things start to go wrong the AI are stuck with these fleets.

Personally I don't find the ships in MTW much "fun". I don't know of anyone else that does either? The battles are very unpredictable and the AI merely spams fleets and moves them around with no clear purpose. It does not try to build trade routes, though it sometimes may seems so (accident/coincidence) this is not the case. I've seen the Danes with a handful of ships on a few occasions. There are enough of these to go from the baltic to the north sea. Instead of doing this however the AI just sends them anywhere and everywhere - isolated and ineffective. This is why whatever we do with shipping, the AI will never use it effectively and the player will exploit it with ease.