My very first class I played and still semi-actively play was a Carnage Marauder (Imperial mirror class of the Sentinel here), and I'm pleasantly surprised at the changes proposed here. I'll be answering both the feedback questions specifically asked about the Sentinel and also the high-level Guardian questions but reframed to be about the Sentinel.
I only seriously tested the Combat Sentinel (both A and B) as that's the class I'm most familiar with, and tried Concentration B (for every other class I'd have to learn the rotation on the live server first to get an accurate comparison/impression).
Reframed Guardian questions:
Sentinel Questions:
As an aside, I've already mentioned this in the "What makes this class unique" section, but I cannot understate how important it is to make Transcendence not use any Centering whatsoever (i.e. it comes with the Ardor utility already permanently integrated). All Sentinels must use all of their Centering for Zen, and an Ability that cannot be used (or is even actively detrimental to use because of the opportunity cost) might as well not exist.
Also, PLEASE FOR THE LOVE OF ALL THAT IS HOLY, just unconditionally give us the Contemplation passive (Resting gives Centering) instead of making us pick between it and other abilities. At this point, it's purely a quality of life improvement that no one would choose because the other PvE option (2% DR and better mid-fight Centering management) actually gives in-fight benefits. I can't judge the other lvl 80 option because snares are almost 100% useless in PvE and I don't play PvP.
To end this on a positive note, I can't help but start theory-crafting when I see the Combat options that weren't available on this build of the PTS: Driving Lance, Rush Down, Transcendence (+Swiftness). Even if it ends up being a complete meme, I really want to try a "drive-by" Sentinel build because that's just my playstyle fantasy when I choose the Combat Sentinel. Speed not just for speed's sake, but actively boosting combat DPS.
Only Combat gives me this ridiculous 30% alacrity boost, and if Combat also added a damage boost based on my current movement speed on top of it, that's basically a dream come true no matter how "bad" it ends up being. Turning Transcendence into an incredibly niche offensive cooldown sounds so much like a Combat Sentinel thing and I AM HERE FOR IT.
(Seriously, Combat B and the not-available options for Combat look like so much fun and I can't wait to be able to freely choose from this tree.)
EDIT: I completely forgot to mention this, but we really do need a better way to gear up, especially if we're going to be doing this for 18 more disciplines. I propose a vendor with the following items for sale: