Osimhen is a far better player. I think the wages issue is being overplayed since Gyokeres, at 27 and knowing this will be is his last major contract, will likely demand high wages too. It might be less than Osimhen's demands but it won't be much less.
One concern about Osimhen would be that along with Mbuemo, Amad and Onana, he could miss close to a month in what will likely be our only real busy period this season (around December - January). That's 4 key players missing at the same time which definitely will have a detrimental effect. Of course, one could argue that not deciding to sign a player only on a month long absence every couple of seasons is silly. But it would be a point of concern.
Nevertheless, if both are available, I would still chose Osimhen.