If I could use an analogy Jon Fitch is the 72 Dolphins not the greatest team of all time but had that special long run. While Koscheck would be the 90's Braves, always in the playoffs strong divisional dominance but never really the best team. Fitch is sort of on the downside of his career, Koscheck still seems to have 3-5 more productive years and I think what happens from here on out will determine who was better.
As for Bisping, how could he be the greatest UFC fighter to never hold the belt when he never even earned a title shot? He's like the Cheick Kongo of the MW division, Cheick is a solid guy with a lot of wins but Cheick steps up he loses and that's Bisping. He's a popular guy but even in his division you could rattle off a half dozen names of guys that were greater.
I don't know if Bisping is quite as far down as Kongo but I do agree he is below Fitch for sure. I don't think simply earning a title shot means you are better though because there are circumstances that go into it. For example Dan Hardy can't possibly be considered to have had a better career then Bisping. I don't think Thiago Alves has either. Certianly Leties hasn't had the same quality career. I think Bisping is closer to Kenny Florian, even though Kenny did get title shots.