You are overstating the degree of his messness and forgetting that Ramsdale was hardly the second coming of Buffon when he was playing. Raya was very good his first few games, some errors have crept in since then, admittedly. What Raya needs now is the support of the manager and the supporters and a run of a few good performances and some clean sheets.
Arteta isn't changing this any time soon. I also read some writer in the Tele recently saying that the 'data' shows that Raya is still performing better than Ramsdale was. No idea what the data is but that's good enough for me