Possibly so but you need to take heed of the situation where it's 5-2 (i.e. United win the Europa). If United win the Europa then we (assume) it's Arsenal and Everton OR Everton and Arsenal. If we finish 7th and United then win the EL we inherit the 2nd EL place which is DEFINITELY Group Stage precisely because England gets 2 Group Stage Europa places.
In fact when the league season is done it will be thus (assume we are 7th) and United are outside top 4.
1,2,3, CL Group, 4 CL 1 qualifier
Europa Group x 2 - E Qualifier (2 rounds)
First scenario United win and not top 4 - now 5 plus 2 with (say) Arsenal, Everton both group stage whoever wins FA Cup.
United lose EL final - remains 4+3 with league position critical (7th we go qualifiers)
FA Cup winner only matters to us if Arsenal finish below us and United don't win EL. If we were 6th and then Arsenal won FA Cup they take our Group stage place as FA Cup winner ranks higher.
What if Utd win EL & finish fifth.
Would the EL place they lose via 5+2 rule be the group spot from finishing 5th? Or the qualifying spot from winning League Cup?
