this sounds like exactly the sort of advice you find dished out by a myriad of folk in online forums who like to regurgitate poor advice but can't actually ride for toffee themselves.I have to unlearn keeping the outside crank fully down. Now I stay pretty level, heels down
You should ideally be constantly adjusting crank position and altering ankle position.
not blindly trying to lower your heels or blindly trying to keep your cranks level the whole time.
Chill out, relax and "play" when on your bike and I guarantee you'll ride far smoother.