Unfortunately I don't think you're geared for Ony 25. Consider that since this raid drops ilevel 245 gear, it's on par with TOC 25 in terms of dmg and gear requirements. While you have a decent tanks set so far, your gear is more at the stage of late naxx 25 / early Uld 10 in terms of overall level. I would say if you want to OT guardians as a warrior in Ony 25 you should at the very least be geared in T8.5 level gear, which is totally doable with just Emblem of Conquest badge grinding.
Also, how long was it taking to DPS down the guardians. Disarming keeps them from using ignite weapon and flame nova, but unless you are killing them in the time of a single disarm, or chaining disarms with other warriors/rogues, then there is a chance that once they get their weapon back they are igniting it and starting to hit you for around 18-20k. I'm guessing fully raid buffed you are not over 40k health, so it's very easy for a guardian to 2 shot you with a buffed weapon if it's not getting burned down fast enough.
I'd say for Ony 25 as OT, you need to be at around 34k+ unbuffed health, and have ilevel 226 or better for all major armor pieces (the ones you can fill with emblem of conquest purchases). Additionally I would try to push your dodge up a bit more. It's a better avoidance stat than parry, and 20.61% is low for an OT trying to do Ony 25.
Also, if you are only OT'ing the guardians, make sure you are effectively using your cooldowns. You'll probably get 3-4 guardians during phase 2, so you should shield wall one of them, last stand one, and enraged regen one, which will lighten the load on your healers.