I also think the same for the Manchester United team who have been playing really badly with no strategy of their own in every important game. The 0-3 defeat at home to Tottenham was very sad and also very painful for Manchester United because apart from the bad impact that Fernandes received in the match, namely the red card in the first half, there were also other impacts that other key players have received as you mentioned. So this will really be a big disaster for Manchester United if they can't survive in the Premier League for another season.
Manchester United defending strategy is so weak and vulnerable that anything can penetrate easily... Diogo Dalot would have prevented the first goal but he was already exhausted and started slagging away from Johnson.
In a counter attack like this, a winger from the opponent isn't supposed to tear up the defense. I've also observed that 2 goals were scored through dalot's wing, but the coach didn't observed that anyway.

I agree with your analysis that the very poor defense in Manchester United's defense line is very questionable, of course there must be improvements in every line that all lines on every side of Manchester United are very concerning and until now, Ten Hag has always forced conditions like this and according to him the players in the squad are good, but it is not according to his expectations and in the end the bad results in every important match do not produce positive results, if this continues then Manchester United's position will continue to fall to the bottom of the standings.