It's not the fact that Sentinels can't take down healers, it's just the fact that it takes marginally too long. They have loads of escapes, stuns and roots to be able to simply spam their healing moves to delay their death by some time. One mistake in the sentinel rotation puts you almost back at square one, while plenty of bad sorcerers can take a long while to go down.
Tbh since I got some expertise gear I'm not as concerned as I was about sentinel DPS, I'm more concerned about the prevalence of CC in every other class. Every other class has some sort of displacement move and some sort of hard CC, we only really have one hard CC and it's one of the worst in the game (can be interrupted and requires us to do nothing during the move). I'd love if we had some sort of reduced CC move, even if it only reduced incoming CC duration by 20% for 5 seconds or something. It's terribly annoying being the focus of all CC just because you have two shiny lightsabers.