>>534418084
That's mathematically not possible unless you lose a fuckton of matches, and then suddenly get streaks to make up for that.
And at launch there were no streak bonuses at platinum and above, only recently did they give you big bonuses for 10+ win streaks at Plat/Diamond.

A quick googke search tells me It took like 700 matches just to get to Plat at launch with a 48%.