The more people you have the more tp moves X is going to use in a shorter time period meaning more healing is needed, buffs don't work on all of alliance so you've got to spend more time rotating or get more support, otherwise your additional players are going to be putting out less and taking more, on top of running out of stuff to kill/wasting more time moving around.
That's why I specifically said:
With proper teamwork and timing
My alliance had no problem with healing. There was practically zero downtime. We camped where no one else did, or we chose a camp where we were the only ones there, so we never ran out of mobs. I was the Brd, and I had no problem slapping Madrigal and Minuet on the extra 2 DD.
(17% lost for adding 1 person is a huge detriment, I don't know what you're talking about)
Not if that 1 person more than makes up for the 17% lost, which in my case I'm sure they did.
It's a silly argument anyways, the point is that I hope they don't include this type of uneveny scaled exp adjustment in FFXIV.
For once I agree with you. xD