2D8 is probably ravager, yes. Given the language involved however, since it's not actually a Monk, it doesn't gain an unarmed strike bonus, its unarmed strike merely gains two sizes over base which don't stack unless your DM is laissez faire.
Since the Brawler's fists don't apply as natural weapons, Improved Natural Attack doesn't work either, which is probably for the best.

The only Breathstealer issue I can see is that they get a +12 to Grapple by level 1 if they're human, and can wrassle and hogtie Ogres most of the time. If your BBEG is going to be anything less than Huge, there's very, very little that he can do if and when he's grappled, since Dimension Door and Freedom of Movement are both out of E6.

At most I'd move the "counts as a size larger when grappling" to Moderate, since the immediate action thing is pretty situational.

For the Battlefist... He could potentially still make ranged touch attacks, but if he hits, he can then choose to pull himself after the fist, making it a sort of super Grappling Hook I suppose? Sounds familiar though...

For the Cenobite, what about "They may use Perfect Harmony three times per encounter" for their Major? At least this way they could do something actually cool, like move + 'port 100' to their target, then flurry with Hammer Blow on the first attack. They get so little from their Archetype comparatively that triple capstone is almost balanced.

Martial Artist: Bear in mind that the Swordsage is a BAB medium class, and the "best" initiator. Perhaps they should be getting manoeuvres as a Warblade in Setting Sun, Diamond Mind and Stone Dragon, with his choice of either Tiger Claw, Shadow Hand or Desert Sun? 6/4/2 with a swift recovery is a bit more reasonable, and since the Swift can be coupled with the Standard Full Attack Flurry that's still pretty sweet. And they can always use Extra Stance and Extra Manoeuvre feats.

Ravager: Pretty well solid really, they can always switch two +6/+6/+1 if they ever need to connect with things.
Should possibly add a clause to stop them from:
- Rend-healing more health than the target has.
- Using it on non-living targets.

I'd mention Minion abuse here, but given all the insane things the Tyrant can do, this barely blips on the radar.

Concerning Engineer versatility: How versatile is the engineer compared to the Red Mage? Serious question.