Not sure I would call it a fundamental flaw so much as a specific one. I mean look at the Cruz fight, Cody was not leaving the same openings there he was vs TJ. Perhaps the personal fued is part of it BUT I think its also a case that TJ's aggression had Cody worried, when your seriously in danger of being finished at any moment though by someone pushing forward its natural to become more aggressive yourself.
What comes to mind for me is Fedor/Crocop back in the day, Mirko was almost always so calm and well timed in his prime yet Fedor had him looking sloppy several times because he was putting him under so much pressure.