Emiliano Martinez might be an option for Man United's problems, but it won't last long because Martinez is no longer young, and from a business perspective, it is also less promising because Martinez's price is still quite high, and it is clear that his transfer value will decrease every year after joining Man United. This may have been a tough decision for Amorim as he opted to go ahead with the speculation by signing Senne Lammens.
Senne Lammens is indeed young and much cheaper than Martinez, but he has no previous Premier League experience, and there's no guarantee he'll perform better than Onana or Bayindir.
There is no guarantee he will perform better than Onana or Bayindir yet but you just have to give him a chance to prove himself at least every player deserves it. Unfortunately Emiliano Martinez didn’t even happen and they ended up with Lammens so they have to make do with the available options with hopes of no regrets when he joins the club.