I guess, here, you're using 'power gaming' to mean 'wanting to play a strictly superior character to the next guy.' I disapprove of that use of the term, preferring to think of a power-gamer like a power-user, someone with great familiarity with a system who can get more utility out of it, to the benefit of all involved. But, using the crass, desire-for-superiority sense, I have to disagree. It's not a guarantee, but the possibility of playing a strictly superior character (even before applying system mastery) that makes random desirable to such a player. The guarantee comes with array & point-buy, and it's the guarantee that /no one/ at the table will have a strictly superior or inferior character, based on stats, alone. If you feel you can only enjoy the game if you play a strictly-superior character, then you simply won't get to enjoy the game, with point-buy or array, /ever/ - but, with random generation, you have a chance of getting what you want, some of the time, you just have to accept that others may get it, instead.
It's really just a campaign-long variation on the practice of spot-light balance that 5e already uses to spread the fun around to players who chose different classes, and a legitimate strength of random generation.