For what it's worth I wouldn't have signed Mount, I don't think he was the most pressing profile in CM we needed. I do think he's pretty good at a lot of things, and I think we'll see that when he's back, hopefully. Although admittedly I don't think he excels at anything in particular.
I'm sure Toney would offer something to any team, even City and Liverpool. He plays the role well. I'm not sure it would translate fully at other clubs though. Brentford lean into his strengths quite heavily, which is why they struggled so much without him. I'm also pretty sure around 1/3 of his goals for Brentford are penalties. Good luck scoring 10 pens a season playing for United, we'll be lucky to be awarded that many in 3 seasons let alone 1...
It just isn't worth paying £60m+ for him when we've already invested in Højlund. It might be worth it for Arsenal, who are actually pushing to win the league and don't have a young striker they've invested in. He could actually do enough to push them over the line.
At United he just wouldn't make enough of an overall impact. He wouldn't make us league contenders. You're better off taking a longer term view and plan to win the league a few years down the line.