This is called confirmation bias.
Theres no way you could actually believe that playing for Roma at half strength from the start and then a third of their strength in the second half due to injuries and subs is the same as playing for Manchester United at full strength
Imagine Lindelof in a 7th placed team in serie A without its captain and best CB Mancini, without its best young attacker (zaniolo), without pedro, then in the first half where the team is somehow winning 2-1 they lose their fill in captain Veretout and their first choice keeper in the first 27 minutes
Thats what that 2nd half was. Remember we lost the first half with Lindelof playing for United
We lost 6-1 to Spurs when we were in much better condition than Roma's and I dont think that one match tells us that Maguire is terrible. How about losing 3-1 to PSG at home missing only 1 player, Shaw. Or losing 3-2 to RB Leipzig, does that mean their 3 CBs Mukiele, Orban and Konate are better than Maguire and Lindelof?