In all honesty how would you compare the online experience of MKX vs SFIV in terms of playability, stability and functionality? You are kinda making it sound like they are pretty much equal in terms of performance.
They're pretty close. SFIV is really sensitive to delay, to be 100% honest. MKX is, too, but IMO SFIV is moreso. So it might have, like, what, 2-4 frames of delay less in my experience, but because the game is super sensitive anyway when it comes to everything, it still feels just as annoying.
As for games that ran better, I've heard nothing but good things about BlazBlue, though if I'm not mistaken, that's largely due to how the game handles inputs in the first place. Even then, I heard it still functioned better than SFIV. SFxT, tbh, was better after the fixes. That's by default, though, being roll back. VF5's netcode is really good, too. It's not foolproof, but it's by far the best delay-based experience I've ever had.
I've always gone to play SFIV, then just stopped because the online was just so annoying, IMO. I am not having issues with MKX, though, because the delay, to me, feels pretty close, but the game isn't nearly as sensitive and I didn't expect much out of the online anyway if it wasn't roll back.