Yeah, even a great player in domestic league can't perform in Premier league, what about Hojlund where he wasn't perform in Serie A. Manchester United don't really need to sign a new striker, they currently have enough strikers and just wait until few matches to see if Rashford, Martial or Garnacho aren't give a good contribution.
But in my opinion, there is nothing wrong with Man United adding a new striker, with a busy schedule next season, relying on several strikers alone is not enough to show consistency in scoring goals. Isn't having other options more flexible for Erik Ten Hag to rotate players? At least they can share a place when the core strike is injured. If you saw the formation last season when Rashford, Garnacho, and Martial were in one game? now the results are not too promising, while the big match awaits in the Champions League, the challenges and opponents faced are different from the English Premier League clubs.