You worry all you want
I won't be, you're obviously too young to be aware of such things but years ago MU were in mid table struggling through almost every season witha good cup run as the highlight of the season, we were still a massive club.
Look at it this was, if say you took.........Parma for instance and you say to Parma "right you're in the Champions League against a big English team, who do you think they would go for first?
Arsenal?
Or would it be more like this Man Utd>Liverpool>Chelsea>Arsenal?
Or maybe "You've got a big German team"
Wolfsburg?
Borissia Durtmund?
Schalke?
Or would they be expecting Bayern?
I think maybe we just have different definitions for big teams, I don't dwell on the past that much so I don't count history in my reckonings whereas you guys probably do, which is fine