I will probably do a longer writeup later, but after being back in EQ for maybe 6-7 weeks, I am really enjoying Underfoot's group level content. Also, yeah, this kind of exceeds the scope of the question asked, haha. However I definitely understand why so many people don't like it - without a consistent group or a consistent guild the expansion would be very very annoying - and it's been a while since we've had an expansion that required a solid group, so it's not something people are used to anymore. (I've been able to do stuff fine with a guild group 98% of the time when my normal group isn't on.)
It is hard, and I am really happy that it is hard. Yesterday, my group wiped three times to a named - then we came back and killed it. Getting destroyed by a really hard named and then coming back and winning is an aspect of EQ that I really enjoyed, and this is the first time it's been possible since GoD era.
My group is usually:
85 SK (me)
85 BST
85 Shaman
often, 84 Wizard
often, 85 boxed Zerker
If needed, an 85 boxed warrior
However many mercs are needed (usually, two,) and sometimes we pick up a bard or an enchanter or a monk.
We don't have a problem splitting in to two groups and popping three mercs in each group if needed, although it's something we only do pretty damn rarely. We started with tacvi/anguish era gear, did boomerangs/monster missions/SOD to get some starter gear, and then we started in on T6/7 underfoot. ATM we're pretty comfortably killing everything in those tiers of underfoot - usually with five characters and one merc - and we're getting ready to start in on the progression missions.
With this setup, it doesn't feel like mobs have too many HPs, and it doesn't feel like they hit too hard. Nameds, with the exception of obviously bugged ones (Hi Merl!) are at, imo, approximately the right level of difficulty. In most situations, mob density feels about right. I think it might be better if there were a few more spots with goo-like trash mobs for people who aren't quite set up to do real UF trash, but other than that, I think it's really pretty good.