some teams are artificially inflating average level scores because they shell out hundreds of dollars on their players Man City style, while the game while the others only spend say 5 dollars a month for 1 player Swansea style.
you will be fine with lower level team provided you use common sense with tactics and make good transactions to get players that always perform well, not all 6 star players perform at 8-9 rating every match. you can win league with a 4 star team with a couple 3 and 5 stars here and there