I don’t know of any comparisons, but anecdotally, I play both piano and button accordion and my guess is that piano keys would be easier for beginners, due to t

I don’t know of any comparisons, but anecdotally, I play both piano and button accordion and my guess is that piano keys would be easier for beginners, due to the direct mapping to sheet music. Beginners start in C major using just the white keys and then added sharps or flats are the black keys. (Then you learn to play in other keys, but gradually.) A chromatic button accordion has other compensating advantages but I don’t find either one easier overall. They’re just different. You get better with practice.