To elaborate a little.

As a class (Marauder, gladiator, pugilist, etc) you get a cross class skill every 5 levels. (10 total)

As a Job (Warrior, Paladin, Monk, etc) you get a cross class skill every 10 levels. (5 total)

With level sync, you only have as many cross class slots as your level allows, so at level 30 in Haukke Manor, you'd have 3 abilities with your Job stone equipped, or 6 if you are still using class.

So yes, if you are running sastasha on a fresh lv15 pugilist (and have leveled Lancer to 34 for blood for blood), your level 15 pugilist gets to use blood for blood almost 20 levels before a lancer in the same dungeon would be able to (even one that is at level 34, he would be synced and not have access to it).

Stoneskin, Provoke, all of the damage buffs (Blood for blood, Internal Release, Raging Strikes, etc) share this availability. You just have to have the class leveled and have a cross class skill slot open.

One thing to keep in mind is the slot#.. Like for example: I have a level 50 scholar (healer). I'm on a job so only have 5 cross class slots (Cleric Stance, Swiftcast, Protect, Stoneskin, Aero - in this order). I join a low level roulette and am now synced to level 20 and limited to the first 2 cross class skills. In this particular case most parties want Protect, so now I have to change the cross class skills to accommodate (Protect, Cleric Stance, Swiftcast, Stoneskin, Aero).