Seems like it's worth it in theory to add an in-form 27 year old striker because strikers are now so expensive and we need to save all our money for at least one CM - and a 2nd soon enough since Casemiro probably doesn't have more than next season at most - and an RCB.
For example, the strikers available on a free this summer apart from Mbappe are older players like Morata, Taremi or Ben Yedder, guys who haven't put it together despite talent like Iheanacho, or I guess Gabriel Barbosa would be the one signing as promising as Guirassy on a free, but who knows if we get him.
We might otherwise end up spending 40M on a Matheus Cunha type, as I doubt we'll sign another 20 year old to backup Hojlund.
Even if he's just a decent backup for Hojlund, for 17M that would be fine, unless his wage demands are Martial-sized. If they're short of that, we'll effectively be saving money at backup striker.
Haven't seen him apart from highlights, but forwards are so expensive now and we just spend a ton on Hojlund, so doing this sort of thing and paying huge fees for a quality #8 and #6 (sell McTominay to pay for the 2nd) and a quality RCB and we'd presumably look a lot better:
Hojlund/Guirassy
Antony/Diallo
Rashford/Garnacho
Bruno/Mount
#8/Mainoo
Casemiro/#6
Dalot/AWB
RCB/Maguire
Lisandro/Lindelof
Shaw/Reguilon or Malacia
Onana/Bayindir
it's not super exciting (still probably need to upgrade on Lindelof, one of the RBs and who the hell knows about how we'll feel about Onana and Antony/Diallo will look in 18 months), but it beats the alternative of spending 50M on another #9 and relying on Mainoo to play 60 games a year.
TLDR: We need to add some quality players to Lisandro, Bruno and Shaw. We have young, discernible talented in Hojlund and our 2 LWs (Rashford, Garnacho) and Mount as a 2nd option as a #10, so a few measured punts at backup keeper, 2nd LCB and 2nd striker all make sense if the money saved from not spending top dollar there goes into the midfield and a partner for Lisandro, and maybe even some saved over for RB, or if we need a RW or keeper.