Bigger/Better ships increase earning potential. You can earn a lot more doing the rares routes in an AspX then a Cobra/Hauler. So there is a bigger gap that balances against that earning potential. Look at the gap between the A-spec FDL and the A-spec Anaconda... hundreds of millions. I think F-Dev was trying for push people into trading and other professions in the mid range. My own path took me thru a bit of bounty hunting, rares trading, pure trading, and then pure combat. Even now, combat and BH'ing pay no-where near to trading or missions. Especially when you factor in time. I can run a passenger mission for 8-10 million in a half hour.. I can't make that even in my totally RNGineered, A-spec Corvette at a CZ, HazRES, or Comp Nav Beacon ( Anymore, I should add. Since they stopped allowing you to stack 20 massacre missions ). Trading supports my combat and exploring. My 200 million credit Python bought my 450 million Cutter, which bought my 700 million Corvette. But that's my philosophy and play style.
As mentioned, there are lots of good ships between the Vulture and FDL. Pure combat ships ? Mmmm, OK, not much there. But there are several that will do pretty darn good.
An AspX is an excellent rares trader or passenger ship and will get you millions if you have rep with local factions. I did a bit of bounty hunting in mine. Engineered it's a fairly tough little ship. One or two corrosive MCs, and a few lasers to strip shields, and it can hold it's own. Just as much damage potential as a Vulture.
Grind rank and get into the FDS/FAS/FGS and they will do the trick. And some trading as well. People swear by them in a HazRES. Very Tanky. And with G3+ DDs, it can actually handle well. More damage than a Vulture, more hull, and better shields.
A Python, at around 110 million, will get the job done until you can afford the FDL of your dreams or bigger. Engineered it approaches it pre-nerf potential.