For lessors or just clearing wins we constantly go with 1 cor 1 brd setups. Usually 11~12 members, sometimes less.

Those BRDs and CORs didn't magically appear, everyone of our members are required to level and gear at least one support job (I have WHM and RDM). This way we can always get the required jobs from our own ranks and only have to invite the minimum from /sh. I know abyssea might have messed with everyone's heads, but FFXI is and has always been about how much support you can give your melees.

You want at least one PT with

Heavy DD
Heavy DD
Heavy DD
BRD
COR
WHM

If your alliance only has 1 BRD then you can have that BRD rotate between the two DD parties to sing their buffs, other party won't be as buffed but songs are better then no songs. Having a WHM outside the DD parties is dumb, they are there to keep your melee's alive and provide support and their primary means of doing so doesn't work outside of party. Curaga III - IV are godly.

The proc party's, aka mage party, job is to focus on hitting procs, this is why we have at least 2 BLMs (or BLM + RDM / SCH). Dealing damage is a secondary concern but it still something they should be doing (BLU, NIN's possibly RNGs).