I had this issue too on the ruby league seeing different colours
The first time i played I could SWEAR that my opponents were playing in lower difficulty.
Having said that, it could be that the distance from sapphire league in ruby league (thus the difference between all-star and superstar level) can be big.
Maybe you (amd I inmy first try) are used to a style of play that is more forgiving but in SS level you can't get away with. Maybe your opponents have played more games in superstar level and they aremore used to the difficulty