Yep there are question marks, but the same applied to Sesko also. I'd say that in a sense there would even have been question marks over Isak (were he achievable)...not the player's ability but the effect on Arsenal of blowing £120M on one player and whether his fitness record improvement last season was a one off...and how it would stand up to the rigours of CL football.
My tuppence worth is that there is a clear dearth of 'world class' strikers available to Arsenal, and we have little choice but to take the risk with Gyokores given that it appears a deal cannot be reched for Sesko. I'd also say that we don't even need a 25 goal a season striker. The people who are running scared of our EPL competition are perhaps forgetting how good our team is already. The travails of last season have obscured the fact that when fit we are a match for anyone, and are in good shape in MF and defence. If we can finish second in the league without a striker at all, even 15 goals from a new striker, plus Havertz staying fit for most of the season will improve us.
Elsewhere - its cover that we really need, and these types of signings (plus Eze) will never really excite but will nonetheless help avoid the problems that beset our team last season.