In your scenario, even if both teams open OT with 99 yd TD drives, whoever won the toss can still win with a walkoff FG, denying the opponent even an opportunity. It's all well if one team starts OT by driving the field for a TD (or FG, or even a lone first down) their opponent fails to match, but if BOTH score a TD, FG, or just go three-and-out, we're right back to sudden deaths arbitrariness: Whoever loses the toss must manage an EXTRA stop just for a chance to win (or not-lose.)
All to avoid the dreaded tie, unsuccessfully if neither team can do ANYTHING for a full 15:00 (remember the 2012 Divisional playoff vs. Pitt?) That's an excuse, not a reason. The NFL managed to "endure" ties for its first 30 years without destroying the game or anyones career. Play 15:00 more; teams can still game the clock for the final possession, but they BOTH can, so the playing field's level, and WHEN the game ends is predetermined objectively, not by who scores last.