It is not a relevant or true indicator of GK qualities, football is not like USA sports that you can watch through stats. Maybe it's the best stat but it's still bad. The only way to actually see who is performing well or badly is to watch games.

No, they don't, unless the ball is closer to the middle and slower. Being taller is irrelevant to goalkeeper qualities, you could use that argument for any goalkeeper if he was tall as Yao Ming he would save it. He saw it on time and moved on time but FK was perfectly placed. Also, keepers in most cases stay near the middle so another bad argument is that he could've saved if he was more on that side, cuz the other side would be wide open. Olise FK vs manutd is an even more extreme example as it was even better and 2 gks wouldn't save it but it had a lower chance so it went a lot against De Gea who literally had a 0% chance of saving it.

So PSxG-G is not a good indicator of goalkeeping and shouldn't be taken seriously