City are probably the top club team right now.
England are about the 8th best National team which is about where we always average. We are meant to get knocked out of tournaments in the QF and usually do. Despite what the press say it’s no disgrace. Given our football playing population it’s about right too.
A few years ago 538 did an analysis of club v national teams and arrived at a top 20. Only 7 national teams made it into the top 20 and their best team was 4th.
If we assume the same now then it will be no surprise to find out that a City player playing for any national side will be facing a drop in standard however small.
What the players do gain is experience of different situations and playing tournament football and, while this is impossible to measure, I would think this outweighs the drop in standard unless they are from a low ranked country that never progress to the latter stages.
England, given the average age of the squad, combined with current ability, have a good chance of being a trophy winning team in three years but we have seen this before and it didn’t work out usually because of club rivalry within the squad and the lack of a top quality coach.