2-Handed Clerics are very viable.
Arbenos' Might is an useful skill, even at Level 1. For a mere 2 mana, you get an extra ten damage. At Level 3, it's an extra 20 damage for 16 seconds (works out to a max of 10 hits in your timing is good, 12.8 hits as a maximum).
Clerics can also switch between 1-Handed and 2-Handed weapons pretty easily. Unlike Warriors, they don't have to invest in shield-only or 2-H-only skills. Some players use that to their advantage by swapping out weapons as needed (fire, silver, matching elemental). Tricky players can even use quicker light hammers to max out duel, than swap to a 2-H weapon with the duel counter still maxed.
There are several versions of a 2-H handed Cleric that does well, but the one that has the most combat potential is the Immortal Build. That build uses Intervention and mana potions to constantly be brought back to life with full HP. Because mana is wiped out each cycle, investing in PER or INT is kept to a minimal, leaving more points to invest in STR. One extreme version was a STR only Cleric. Seemed a bit freaky. Obviosuly, that type of build will fail a lot of trait checks, but it can be fun to role-play a single, minded crusader.
Overall, since Clerics use healing powers to stay alive, they are less dependent on the use of a shield. Players might see an advantage in using 2-H handed weapons for the extra damage as that is one area Cleric's can suffer. Arbeno's Might is just icing on the cake for them.