Except his reactions are generally fine. His save percentage is higher than most keepers in the prem. People are more pissed off cause of his errors, and understandably so. Those however are just as likely to be due to first season anxiety as much as anything else. I think it's something he will get better at because historically, he hasnt made this many errors!
Look I get it, it's so easy to look at it and assume he will not get better, but there is a few things to consider here. The first is, we absolutely have not been set up to maximise his strengths. That is as much to do with personnel as anything else and hopefully, in time, as the squad is turned over, that comes to the fore. You have to look at the bigger picture and not just the last three months. Where is our playing style heading towards in the next 2-3 years? The younger purchases like Martinez, Mount, and Onana, hojlund plus players like Mainoo and garnacho coming into the team means that we want to be better technically and be able to pass more . The limitations of most of the other players in possession and intensity means our performances are wildly inconsistent. Simply put, the individuals in the squad don't have complimentary attributes to execute a style of play that is consistently good. So we must commit to building a squad that can execute a style of play, otherwise the next manager comes in and wants a change of style, so no longer sees value in playing martinez, onana and mount. This is not sustainable. We have to commit to this and see it through, regardless of how painful it'll be. I've seen enough decent passing to think, with a little more confidence and more complimentary players around him, he will come good.
The second point is, as far as I can tell all goal keepers are making huge errors. Look at the arsenal keepers, they have been terrible. Alisson has made several mistakes, as has Edersen and the new spurs keeper. But the big difference is their forwards have scored double what we have so there's even more pressure on our backline to not concede. The grass is not always greener.
If there is a golden opportunity to bring a keeper on the cheap to compete and replace Onana, then sure, let's go for it. but the reality is. if we deem him surplus to requirements then we will not be able to recoup what we paid, meaning we won't have much money to buy a new gk especially given our ffp troubles. Whether you like it or not. He is here to stay so rather than putting him down, it's better to put up with these teething problems, get behind him, and believe in the longer term planning of the squad.