We were never intended to have access to even smaller capital ships, and none of the vessels we can fly are dramatically larger than the bigger fighter-class vessels.
There is a bigger difference in size between an F-15 and P-51 than an Anaconda and a Vulture, or a Corvette and an FDL.
That may be true if your definition of not being dramatically larger is 10+ times as large. i'm sure you've seen this. This gives you an idea on 2d size differences from overhead. You then have to consider the height differences, or you could just look at mass too.
http://imgur.com/iX2Q7Ko
The ships i'm talking about not being able to keep up with for fixed weapons to matter is anything smaller than a python ...which is about half the footprint of the conda. I'm not saying it needs to be as slow as a cap ship or so slow that it can't even be used to fight against other ships of the same size. It should just be slow enough so that fixed weapons aren't an option you can just rely on being usable against basically all ships in the game. More than half of my weapons are fixed and the others are gimballed. i have no problem killing ships from sidewinders through vultures. I shouldn't be able to. They're tiny and I should have no hope of lumbering my ship that's many many times their size to get my fixed weapon on their tail. But i can. And i do. And they all die. And i feel no different flying that ship than i do a vulture or FDL (i haven't flown anything else in a couple years except my ship fighters).
It just needs a little push towards being slower to maneuver. Just enough to make turrets matter and then they can address the other things that go along with that and a new type of flying behavior is born and all the strategy and options that brings to the game.