Arteta's change in system (read copying Pep) since 22/23 is partially to blame for his drop-off.
Martinelli is not Grealish. He's more explosive and direct: more of a wide forward than a midfielder. Moreover, he's young and raw. So, asking him to play a more technical role where he has to start wider, beat more players and pass/cross more than shoot is not playing to his strengths.
I remember a CL group stage game last season against, iirc, Sevilla, where Martinelli had the opposition full-back on toast. Beat him multiple times, I think the number was in double digits. But every time he did so, he crossed rather than shot. That's not his nature, I believe it comes from the manager.
Yes, he's been wasteful recently, but Arteta's system isn't helping (him). Maybe a move would be best for both parties?
PS. The comparisons with Antony are laughable.