Brighton is one of the teams that is able to make it difficult for big teams to achieve maximum results and if you look at their current performance it is very consistent. They could beat Manchester United quite easily considering the many problems Erik Ten Hag is currently facing. The three Brighton players you mentioned are devastating for Manchester United's defense and especially Karou Mitoma will definitely be very difficult to stop because he has speed and good dribbling.
Brighton are not a very big team, but they're not to be underestimated because they could take you by suprise and win with a very good goal margin and for some seasons their performance in the EPL has improved alot and they're currently becoming a threat to some of the bigger teams especially Manchester United which they've been very tough against for the past two season.
Manchester united are not in a very good form currently and could cause a problem for the Manchester United defence, especially their youngster that's in a very good form this season, Erik Ten needs to come up with a solution to make sure United does not suffer another lose again and they should be lucky Aaron Wambissaka is not among the list of injured players currently cause he'll be very reliable against Karuo Mitoma.