If your warrior can't outdamage and outsurvive a raising colossus in PvM, I strongly suggest that you take a serious look at your build, armour and weapons.
And drop by the warriors profession forum here:
https://stratics.com/community/forums/uo-warrior.422/ to get ideas on weapons, armour and builds.
All my warriors shine over my mystics in PvM, and with warriors, you don't have to bother with the headaches that monsters with dispel cause to mystics.
RCs also have a very short duration and cost a lot of mana to cast. Even with 120 focus, good mana regen, studded armour for 55 LMC and plenty of mana, you will run out of mana middle fight with some monsters, causing you to have to rely on invisibility (a mage spell) to break aggro and regen mana to cast it again. For several monsters, you better have spellweaving along to cast arcane empowerment and word of death, because your RC will get dispelled a lot, and it lacks speed to deliver the final blow.
It is specially annoying against greater dragons and ancient wyrms. Frost dragons are just plainly out of the equation without spellweaving.