To maximise the squad we'd need a player who offered something distinctly different from Jesus at least. To me that means: over 6', greater athleticism and foot speed to give us a genuine counterattacking faculty, a more direct attack on the box (less "false"), and world class finishing ability.
Nketiah is marginally better than Jesus on height, athleticism and directness, but still clearly isn't good enough. I'd say the last thing we want to do is sign another player in his bracket.
You can therefore see why Arteta wants Osimhen: he's 6', leads counter attacks brilliantly, works extremely hard off the ball, is capable of creating chances for others, and is the quickest player in Italy. Yeah he'll cost over £100m, but in this market that's Rice quality at the Rice price.
Osimhen at Arsenal could allow us to consider an option other than Martinelli on the left. At the moment, despite his critics, Martinelli is the only guy we've got who consistently times receiving runs behind the defence, as he did countless times against Brighton.