Question was not about starting 11 but full 23 players squad. Because more than likely one player will not go to EURO from this group.
It is not hard to guess that Southgate will take Mount because he usually starts for him and Maddison has not been in the squad so I think he will not go even tho he should.
You have 3 GKs, 6 front players (Rashford, Kane, DCL, Sancho, Sterling and Grealish), 8 or probably even 9 defenders because England play with 3 CBs and 2 wing backs.
This leaves 5 MF places. Rice and Henderson are certain for deeper role. So for 3 places you have Mount, Foden, Maddison, Winks, Phillips, Ward Prowse...
Going with just 2 DMs or CMs who are more known for their defensive work is not serious option so this is why one of Phillips, Winks or Ward Prowse will go and is always in the squad.
And now you have Foden, Mount and Maddison for 2 places. This is why all this discussion. Mount for England just like now for Tuchel plays as one of the 3 most offensive players on the pitch. And this is why some people like Austin here say what they say because they look at the numbers:
Goals in all competitions:
Foden: 10
Maddison: 9
Grealish: 7
Mount: 4
Shots (Premier League)
Maddison: 47
Grealish: 46
Mount: 43
Foden: 28
Assists in all competitions:
Grealish: 10
Maddison: 7
Mount: 5
Foden: 5
Also they all played 400-500 minutes less than Mount and Masons 4 goals have been against 4th division team and against 3 teams that will play Championship next season. 5 assists - 3 from corners and one against Championship side. They probably think this is not enough for one of the 3 most offensive players on the pitch.
But the only problem here is Southgate because he plays wrong system for this amazing group of attacking players.
They all should go imo. And with 4-2-3-1 or 4-3-3 there would be place for all of them.
But with 3-4-3 you have 5 defenders and lets say Rice and Henderson in double pivot. So only 3 places on the pitch for Kane, Sterling, Sancho, Rashford, Grealish, Foden, Maddison... Southgate is clueless...