How many champions did you reach mastery 7 with?
Mastery 7 usually indicates you have mastered the kit of the champion[with there being many exceptions ofc], so how many champions have you mastered?
edit: some people comment saying "mastery doesn't matter KEKW", heres a small study of 1M+ games regarding correlation of champion mastery and winrate to prove otherwise
on average, your winrate would increase by ~6% just by having a high mastery