His shot stopping stats are so odd. After today he'll probably be 4th best in the Prem, and top 25 in Europe. But he's made numerous mistakes and he doesn't make that many memorable saves. Despite that, if the season ended today, he would finish with a better shot stopping stat than De Gea had in any of his last 5 seasons (though the stat can and will go down as well as up over the rest of the season, so no chickens counted).
I might dig out the detailed stats if I get bored this week, but it seems like he excels at the routine stops, which add up a lot more than it seems. Despite the phrase, there is no such as thing as a save a keeper is expected to make. All keepers let saveable shots in. What matters is how often.
If you looked at De Gea's stats in his final few years at the club, the mistakes weren't the problem. The issue was how often routine shots got past him. Not out and out mistakes, maybe not even ones you lament as "should do better". Just shots where the best keepers are saving them 70% of the time, but he was only doing them 40% of the time. It meant that he rarely got above average in his overall shot stopping stats.
Feels like Onana is the opposite, doing the routine but unremarkable stuff well at the moment, which is adding up to decent stats overall. But he's disappointing fans with really bad mistakes in key games, and not making the kind of flying top corner saves that has fans going away purring.
Combined with the fact that quality passing is a bit of a hard thing to quantify for a keeper, I'm willing to bet that Onana will struggle to ever win fans onside, no matter how good his shot stopping stats end up being.