Its quite a basic thing to judge opponents on their team% but you should never do that cause although their team looks weaks, their players might be good (for example he might had a 40% player but with crazy stats like having over a 100% at some places while having 1% at other places. Also you need to understand that there always that odd factor that for no reason u can lose or draw to a weaker opponent.
Its often disapointing but you can only get use to that as it will happen countless times.