In pre-made PFs, I seen 3 healers, 3 Tanks...just about anything. Sometimes this done to carry 1 or more members thru easy fights Hm primals , early Coils and some DFs. I like the idea behind pre-made non-standard partys. In fact, while I was learning Scholar at lv 50 I had a friend come along as Whm to help me heal Ak. I'd never healed a Df before. It worked for me.

Fun fact: I've cleared Ak and WP without a Tank,thats 1 Bard, I Whm and a Nin. We rocked!