They did
You have 2 options in battlegrounds now
There's nothing to fix. It is an open competition, so you face whoever comes your way. If you want matchmaking tuned to your account, then you can play unranked BGs as long as you're willing to sacrifice the rewards that you're not willing to face larger accounts to get.
It’s indeed bad. I’ve got no idea how they make the difference of matching mechanism between unranked bg and ranked bg. Yesterday I brought only 7r1 and 6r5, tried unranked bg 5 times, only one time my opponent had the similar level of champions. For the rest of the time my opponents were carrying all 7r3 and 7r4.
Unranked is based on your prestige, not your deck prestige.
And the worst part is most of times you have to choose first against 2 or 3 times bigger than yours... They don't care about f2p players