Everyone is thinking the same like you. Turkish league could be an easy place for him to beat, but sometimes, Reality tells us the harsh result. He moved to a less competitive league. But, he will have lower quality teammates. This doubts me if he is gonna score numerous goals for Galatasaray.
About Osimhen goes to Arsenal, it's unlikely to happen. Napoli has sent them an offer to sign him in June, but they refused it due to the non sense price and expensive wages. Also, it's no way for them to recruit someone as problematic as him and his agent in their squad.
Arsenal did the right thing not to sign him from Napoli.
I believe the news is fake. Osimhen’s transfer is hot news right now, sports media are probably making things up to increase their ratings. Chelsea and Arsenal could not sign Osimhen because of the expensive contract, if Osimhen had accepted a paycut from either of these clubs, he would be in the premier league.
Osimhen is going to score a lot of goals at Galatasary. The team is not a weak side, their attack is very strong. Yesterday, they won their match against Erokspor with a 8-3 scoreline. Scoring goals at Gala will not be a problem for Osimhen.