On one hand that may be what Mbeumo feels but on the other hand I think it is a little bit for Manchester United to be able to bring in Mbeumo because of the competition from Tottenham who also want him so Brentford will certainly consider an offer that is profitable for them.
For Mbeumo, he also has to think about his future, Tottenham will compete in the UCL next season, that will certainly be an attraction for a player who wants to develop further while Man United is in a slump in the last few seasons which makes a player think more deeply about joining them.
United will have to make a good offer for Mbeumo if they want to attract him to the team. Because Tottenham has the advantages you mentioned, and it all depends on the best negotiation for all parties. Brentford will certainly want to get the benefit of selling Mbeumo. If price is not an issue for both teams, I think Mbeumo will consider Tottenham for the Champions League. What will United offer? Maybe a bigger salary, or they have other ways to get him.