It's a fair point. Teams can push up and squeeze play much more effectively when they aren't worried about a ball played in behind them - believe it or not, it's not the goals from Lukaku that I worry about losing (I think we'll spread those round with much less of an issue than many think), it's the pace and threat of being able to score on the break with a relatively innocuous ball played over the top or in behind. Bolasie's injury exacerbates the problem as he also gave us that option. Sandro is fairly quick, but not blisteringly quick, I do think a Demarai Gray or (whisper it quietly) Theo Walcott would be a big plus for us. Not being addressed this window though, it seems. We'll have to rely on Sandro and wait for Bolasie's return
I've stated my points about Gray above. I'd like him here but at the same time I think Lookman is a very similar player.
But yeh, I'd take Walcott too. I don't think we've got a chance of signing two players from Arsenal, though!