Don't let the laughable cluelessnes that some people on the Caf exhibited back then trick you into thinking that Neuer was ever controversial amongst his clubs. He wasn't. The most controversy his employ ever saw was a small group of Bayern ultras who questioned the unprecedented transfer sum spent on him and declared that he wasn't needed, their own keeper Kraft back then was also good enough. It was honestly weird and backwards how a very vocal part of the Caf kept going on about his style being suicidal right up until he won the world cup, when everyday evidence clearly showed the contrary. I do quite vividly remember those discussions, even if I was just an unparticipating lurker back then.
But back to Onana, it should be unquestionable that he's not sustainable in goal. It's not even about non-quantifiable things like trust, he's a hazard by every metric.
The only question for me is whether United wants to replace him outright and buy a new #1 directly, or if they'll replace Bayindir (who is equally not good enough for his position) with someone quality enough to challenge Onana for his spot.