Length is one thing, size is another thing. It sounds like you're referring to ships of a similar size but different hull lengths, but a 100 ton schooner will be much faster than a 1000 ton galleon, there's just no way around it. I'd hope they continue to expand the types of ships to allow for more types of boats like speed cutters, there is so much untapped potential, but I think with the current dynamics of sailing it wont matter. Ships come in all shapes & sizes, but the galleons in game are like 15x the size of schooners. There is no way they would be faster than a a schooner & yes; in a game you can pick & choose what elements of reality and fantasy you have. It's my personal opinion that implementing this element of sailing will improve the game. You don't have to share that opinion, but you are wrong about the dynamics of sailing. While you are wrong, I'll respect your right to be happily wrong.
I'm not a sailor, but I did stay at a holiday inn...