Naw, Roland has an easier time than Mordicai just be sure to run both Quick Charge AND Stat and use them to help sustain yourself (killing them damn minions and healing for it OP).
Because of Crawmerax and Knoxx, my solo Siren evolved into a build where speed, health regen and my action skill where my most important talents. It’s almost the same tactic for both fights (with Cramerax having the added difficulty of needing hit the back). If something gets too close and/or my health gets too low I zoom to the other side of the map and hide. Then I come out from cover only once my action skill is ready again and I take more potshots at the boss or the mob. Because of this I finally discovered that a class mod that reduced my action skill time was more important than a DPS class mod. Also, for knoxx sometimes I literally needed to use equip a gun or classmod that regenned ammo.
Wow. He made Craw look like a chump.