Honestly think there's some dramatic tempering of expectation levels required here
Do I think Weghorst would change our fortunes dramatically? No
Do I think he's better than Maupay or Simms? Yes
Would I be happy if he were the only striker we signed? No
But we have to bring in (probably) a reserve keeper, a left back, a centre back, at least one centre mid, a wide player and a couple of strikers this summer on a budget of next-to-nothing
There's going to have to be some compromise along the way - for instance, we don't need to sign two strikers who are as good as or better than DCL - one of them just needs to be better than Maupay/Simms and the other needs to be DCL level.
The main arguments I'm seeing against Weghorst is his record in the PL - he's scored twice and assisted 4 times in 37 appearances in the PL (although it works out at about 25 full games), not great numbers for a striker, but he played in midfield a fair bit for United at times and, for all he misfired in front of goal, he does have some attributes which are useful - there's a YouTube video somewhere in this thread of his highlights from one game which give you an idea about what he brings to the table.
If he were a loan and coming in alongside another striker, I could see the logic in the move. We will not be spending money on every player we need as we don't have it, so loans and frees are going to be important this summer. Having said all that, I would be surprised to see Burnley loan him out again, so it sort of becomes a moot point as I wouldn't want us spending actual money on a 30 year old