Parmandur
Book-Friend, he/him
That's probably why it is an option: by the atandard rules, movement is more or less irrelevant, which is well and good. Adding the variant gives some purpose to movement, by a little bit, but doesn't make Advantage much easier.I agree that a Rogue should be able to Sneak Attack every round. I'm ... less convinced about Advantage.
As for Flanking ... It's so easy to move around an opponent that it becomes a costless way to get Advantage, making any way that requires any cost-benefit balancing irrelevant. (At least, in my experience, running with the Flanking rules.)