The problem with any short term signings is primarily the fact it'd take them a long time to settle in like with most other players that sign for us.
Say we had signed Ings when he was available as a 1 year placeholder. He'd take a few months at least to bed in. Problem is, he's not good enough for us to shoehorn him in like we would with Kane or Haaland. Which would only serve to drag out this process. On top of that, there'd be a lot of games where he really struggles (being on the bench won't help), and I'm not sure people here would be happy to see it.
Then at the end of it all, once they're ready, we replace them with the better option. But then if they're going to be stuck on the bench what makes them a better option than Jesus?
We don't do stop gaps for a reason.