Yeah that's totally the same as losing 3 of your top scorers at once as well as your best midfielder this season.
It's the equivalent of Salah, Mane, Firmino and Wijnaldum all being out at the same time. Teams can cope with defensive injuries if they have firepower, I'd swap having Kane, Alli and Son out anyday for Vert, Alderweireld and Trippier.
If you have lost your entire defense before you would have said the opposite really.
I had seen United defeating Arsenal under LVG with an almost entire team out and having to play Carrick in defense, something that also happened under SAF several times too who put Carrick and Fletcher in CBs at one point.
Injury crisis happen in any big club and we had our fair share of it. The role of the manager is to get on with it. You're acting like it's an easy ride with squad and injuries in other big clubs.