Whatever the gameplan was supposed to be (offense or defense) or whatever it COULD have been, it doesn't matter when the players aren't prepared for the higher intensity of the playoffs. This was a choke, and I feel more troubled by it a day after. And it was a "complementary football" choke between the offense and defense (Daniels & special teams were good).
That's the head coach being a great reactor to adversity in the season (a lot of the adversity of his own making) and a poor attacker. O'Brien has never much forced adversity on our opponents that they have to respond to. He just doesn't seem to have that strike-first mindset. RAC has done that well himself. Tom Brady was a red-faced crybaby in the first half of the playoff game two years ago due to RAC.
And O'Brien himself reacted badly to the adversity of this game, desperately going for it twice on 4th down in the first half? It's like when he desperately went for it on 4th down in the Eagles game instead of kicking a FG. Then we lose by 2.
Those games were beyond O'Brien, as was the KC playoff "game." He's won the AFC South 3 out of 5 years with mostly trash QBs.* But he's not mentally/emotionally able to juggle coaching and play calling. Kubiak and McCarthy are available (for now), and I think they'd be fantastic with Watson, but I see O'Brien as too delicate to hire a possible competitor to his own job.
*All AFC South teams were in the top 12 in defensive yardage allowed in 2018. So to win 11 games and the division IS an accomplishment. One of the top two divisions this year, IMO.