If what you said about IF was true, Bap’s playtime would be significantly higher. But IF is far, far overrated. To start with, it does have a cast and an arming time. I’ve been killed because the cast and deployment didn’t complete before the damage arrives. Dead Bap. Second, it’s actually a pretty buggy ability. I’ve successfully deployed it to save from things like D.va bombs, only to die inside it anyway. Yes, fully inside it. Yes, team there with me, I was the only one to die, right in the center of it.
Next, even if it does work properly, it’s nowhere near as good as rez. But they operate in different niches anyway. Assuming it does save you - you’re now at critical health in a known spot with nothing to stop follow-up attacks from finishing you off. Even stray shots in deep falloff can kill you.
What IF can do is prevent a teamwipe during certain ults, but that’s very situation dependent. I’ve seen clever Junkrats hold riptire at bay until their team shoots down the IF field, or just wait out the only five seconds until it’s gone anyway. In a way that makes it the opposite of Ana’s nade - the anti-nade has the potential to negate a Zen ult, while IF has the potential to negate a rip-tire or D.va bomb. In practice though, if IF were that good, he’d see more use than he currently does.
All that said, I’d be completely fine with IF’s removal if it meant we got a more useful utility in it’s place. Right now it’s the worst of both worlds - vastly over-estimated by critics, and vastly under-performing in reality. It’s a mediocre ability that people think is OP. So you know what? Just toss it in the garbage. Supports live or die by what utility they can bring in this game, and Bap just doesn’t have any meaningful utility to bring right now. His ult is one of the worst in the game and has a hard time synergizing with anything. And his biggest competitor, Ana, has vastly more utility and a versatile ult that synergizes enough with several different heroes that she’s almost always a right choice for the map and comp.