How would you describe Leicester's squad? They're very close to your average. About the 6th-8th best squad in the league. But they won the league because they were well coached. If we had a semblance of management last season, we would've walked the league. Given how things are in flux for a number of teams, it is possible to win this premier league now with an inadequate squad, as long as you manage it well. This is possible because there are about 10 bad teams in the league, and another 5 or 6 we should feel confident of beating every time if we are well organised and healthy.
The same cannot be said for Europe. Once you get out of the group stage, you face a gauntlet of the best clubs in the world. If your squad is of average quality, you will not win three straight rounds against Juventus, Barca and Bayern. Make sense?