I think the question is, which skill set suits Arsenal right now, and going forward?

It’s pretty clear Raya is better on the ball and picking out a pass, yet inferior to Ramsdale on intercepting crosses. But what attributes do you value most between the two? Neither offers every quality you want in a keeper. Furthermore, both Leno and Martinez were better shot stoppers than either Raya or Ramsdale.

Arteta is looking at the whole team, and picking the keeper who best fits his system.