I'm not gonna lie, if I have my way in this world I will have one of each (not perhaps a full blown Ultra4, but the basic concept of what you can get along the lines of an EVO1-like setup).
I don't really see them as a comparison; two different animals. But to force a comparison, I think you can objectively look at what happened at KotH this year and catch the drift: Bobby's bouncer absolutely crushed the Backdoor Challenge time in a way I can't fathom an Ultra4 could do.... but on the other hand I couldn't fathom a bouncer making it 9 hours in the full format race events and finishing.
I will say that, other than when things go wrong, the bouncers aren't nearly as chaotic as it seems. Watch enough regular vids that aren't focused on the crashing and you'll see that it has its own finesse and predictable handling that to me reminds me of watching those crazy drift racers... looks like chaos, but really isn't.