The problem is hybrid classes do just as much damage with far superior utility.
Example: Scoundrels have tons of CCs, stealth, superior vanish, 30m range options, HEAL, ranged instant AOE on a 6sec CD, AND do equal amounts of damage (if not superior).
So it's not L2P. Sure some people finish warzones with good results as a Sentinel... but let's get real here. Those same players would most likely do exponentially better with any other class.
Also, I find all the counter-posts that claim they **** with sentinels (there's even a thread posting warzone scoreboards) pretty humorous. Love it when Sentinels think they are unstoppable wrecking balls when they are oblivious to the multitude of healers spamming heals on them. Or could it possibly be that you're not that great and had a good draw and went against really bad players? Hmm nah, feeding your ego is the more logical answer. Amirite?