Manchester United, on paper, are a better team than Tottenham but this is a final, everything could happen. Few years ago, when Tottenham were going to play the Champions League final against Liverpool, everybody was sure that the Reds would easily win and well, they did win but it was not an easy match, at all. Finals are quite unpredictables.
I don't see this to be honest. Manchester United are better than Tottenham in terms of what? Their conditions are both bad in domestic competitions where Tottenham are currently in 17th position and Manchester United are 1 level above them in 16th position with a difference of 1 point so in this case they are comparable.
In terms of h2h, Manchester United facing Tottenham is actually not too good where in the last 5 matches even Mancheester United can only win 1 draw and 4 defeats so what makes Manchester United a better club than Tottenham at the moment?

I don't feel that Mancechster United are superior to the current conditions even though their chance to win is clearly very much there because indeed maybe the consideration is to the big name and previous experience but that does not guarantee now because everything can still happen including in the race for the trophy this time.