The biggest issue for a columi group is the DPS. I have not tried post 1.4 SM and cant remember if they made it easier to beat enrages, but before the patch a full columi dps group could have trouble at some spots. Tanks and healers have it pretty easy in columi compared to dps. With that said though it was clearable as long as they knew good rotations and could save themselves when possible (watch for mechanics).
Now with the nerf I imagine it's not too hard at all in columi.
It definitely was, but they have made changes to lower the requirements.
Toth & Zorn
•The amount of time before Toth and Zorn enrage when one dies has been increased.
•The enrage timer for the encounter has been increased to 6 minutes 30 seconds.
•The enrage timer for the encounter has been increased to 4 minutes 30 seconds.
•The time before Baradium Bombers explode has been increased.
•The enrage timer for the encounter has been increased.
The baradium bomber phase was by far the toughest DPS check. Even well geared teams could have trouble if he spawned in a bad spot or you were just a little slow in picking it up.