Also consider this: We live in an age of rapidly expanding tech and break throughs. Now imagine that we come to a point where there's not a whole lot left to discover. Really, all the ships do the same things. Enable us to travel faster than light and thus across the known galaxy. Innovation will stagnate, and really all the classes of ships do is just get bigger. Certainly the smaller ones are more maneuverable and capable, but that doesn't change the fact that humanity has an obsession with sticking with what is cost effective. I mean, we certainly could make newer, better ships; but who has time for that when there's money to be made in other markets and to continue to milk a perfectly good cash cow.
There were patents for huge innovations in the automotive industry made in the 1970's, but after the energy crisis stopped, all that got buried and sweapt under the rug. Did you know that we could make cars rust proof and it wouldn't cost anything extra on the consumers side? No? Yeah, thank the corporate dinguses in Detroit for burying that patent. Also, vehicles lasting ages isn't unheard of, I mean look at how long we used horse and buggy as a species. Thousands of years, and plenty of countries still use them in day to day life. The original VW Beetle wasn't taken off production lines until 2006, and plenty of places still use these cars as taxis, police cruisers, or just in general for civilian use.
The romans used largely the same technology throughout their reign, so is it so hard to believe humanity would use something for hundreds, if not thousands of years?
I don't have as big an issue with it. I just assumed that humanity is stagnant in innovation now. I mean, it makes sense. How can you make something newer and better when you've already got a handle on that?