Nketiah was doing very well before Jesus came to Arsenal. And Nketiah also did well in some Europa league matches he was privileged to feature. So I am not surprised that he did well in the absence of Gabriel jesus.
How long will he be out? Last I know was like 3 months for the injury and it has been nearly a month already since that was said, which means only 2 months left. If that timing is correct then they shouldn't really get someone for only 2 months absent. If they could hold off for 2 months that would be better. However, if they are looking to get someone for long term, like even if Jesus was healthy type of deal, then it would be reasonable for sure.
These timings are so far. I don't know why football injuries last long. Players like Benzema, Mane , Pogba, Kante etc are supposed to be back and playing by now.