Mdk: I disagree. I think anyone above 6 can be a very valued member of the group if you play your cards right.
I disagree too. My group usually has 2-3 extras and I make it a point to equip everyone with Magic, Ability, SJ and Weapon.
Thankfully, one of the extras will be a RDM (myself usually) since I am too busy distroing cells to keep up refresh and haste cycles. Best part is the side part can take part of cells by itself. For countering madames, I usually go RDM/DRK while the main RDM goes /WHM.
RDM with full cells can solo Puks and Ziz (need to watch petrify though, best to have 2 people) so side party can split off early to do Puks or slightly later to do Ziz. MNK with full cells on 1F can solo anything so I send 1 to kill extra Raptors after mid-Raptor room done...Nowadays my group does a 3-way split with more than 6 and 2-way split with 6. Usually we manage to get enough cells for everyone in about 15 min. And no particularly relic equips either.
Other jobs that can solo include BLM (slow due to MP issues) or BLU. Pure melee jobs will require some potion supplies.
However since we added 1F madame to the fray (by clearing Puk wing), we now take about 25-30 min to clear 1F. In the time the main group takes to clear for extra SJ, my solo mnk even has enough time to clear out half the Puk wing

The other teams will go join him when done with their own tasks. On the way, we also hit some Mamools to see if we can get fanatics for 5F.
The way I see it is you'll get back the extra time invested pretty quickly. Madames become easier, and regular mobs become cake. Furthermore, everyone can enjoy the full benefits of their job (minus being naked) and not be bored to death in the 100 min, so why not?
And 1 THF, 1 BLM can nail all the gears in the first room of 5F without death and no fanatics. Just remember to /logout at the top of the stairs. Always simpler with fanatics though, about 25-50%? rate on 1F Mamool chests.
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The 6F Ramparts in the side rooms doesn't appear to link with the chariot or gears. Or loses aggro real quick even if it does. If using the flee > lose aggro method, can try running into the side room first, before hugging walls in the big room. I tried once on RDM with 2 powder boots. Lost aggro on everything at about the same time the 2nd powder boots wore off.
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Madames went easy on us today, so we had 26 min to spare after clearing 6F Madame.