Again, I already said it to Kore and Wursti for the last nations cup. If you want to do an European Cup with nations, it should be the best players of each nations that play. Otherwise its just a normal tournament where people play with those who have their Nationality.
I wish we had a name for such a tournament. Perhaps a Nations cup such as NWWC, maybe something like ENWC would be a cool name.
Regardless of the haha funny sarcasm:
More teams more people more fun.
A lot of good players would not get a chance to play because of roster limits. Especially for your own nation and ENG.
It also allows for teams that are less serious and tryhard, and are just participating for fun.
If you're scared about team FRA splitting up into two teams of equal strength then it's up to your captains and players themselves to make one strong team. If some good players from your nation don't want to play for your nation's first team, then that is their choice. You can't force them to play for team 1 if they'd rather play with their friends in team 2.