Considering the level of inconsistency in the Manchester United team under Erik ten Hag, I don't think there's anything wrong with your opinion is absolutely valid. If Manchester City or Liverpool were to be the team that's facing Southampton this weekend, I'm very sure you'll have a different opinion but because it's Manchester United, there's every possibility that they'll be beaten by the Saints.
It's easy to tag the Red devil's to be one of the weakest teams in the EPL at the moment, but after seeing some of its players put up a good performance in the international games...I have a feeling this could be a turning point for for the Red Devils...and by the way it's not like Southampton themselves are in such a good form that it could guarantee them that victory that is being talked about, they need to put in the work to get a goal!
The funny thing is that I do not think that they are weakest, but I think they can be. The issue is that Doncaster was right, they can win this game 5-0 and I wouldn't be shocked at all, United has what it takes to beat Southampton that easily, and it wouldn't be a shock to me if they do get a win like that, but if they lose, I wouldn't be shocked at that neither, both look quite possible.
I mean sure City could lose to some small team too, but that would be a shocking result, everyone would say it would be unexpected to see City losing, it is not unexpected to see United losing, nor winning, both are equally possible. This is the problem that they are facing right now and I have no idea what they can do to stop that, it's definitely an issue. I feel like the best thing to do right now would be just focusing on what to do, and it would be something that could make a good return on betting, I am avoiding betting on United for a while longer, it's the best way to protect myself.