Since I have played this map a few times now, I thought I'll share my thoughts with you.
After trying Campaign Nightmare 3 times, I gave up because I got crushed at wave 1 or 2 due to the low building time. I also can't build in the combat phase, because I need a DPS char to kill the ogres before they kill my minions. After that, I tried Survival hcmm which turned out okay (Summoner 1800/2000/600/1800, Monk 1300/2200/1900/2000). If I hadn't died at wave 16 through a stupid jump I probably could have managed to hold the build until wave 20. The main problem I was facing was that on the top layer up to 10 ogres (half copter-ogres) were torturing my archers and my mage. Ten ogres reinforced by copters are far too much, they kill my defensive row of minions in about 10 seconds if I don't help them out.
Afterwards I tried Campaign again. This time I managed it, because I got lucky and no sharken or whatever ran behind my defenses and attacked the crystal directly like they used to do in earlier games.
But the map definetly doesn't work as jump pad from mid-game to end-game, since it is practically impossible to do Campaign without a good DPS char/pet with 1000ish stats, which actually is possible for Mistymire, Moraggo and Aquanos (excluding the bosses).
To put it in a nutshell, we definetly need more time to build during the build phases, or just much lower mob-strength/speed/health (I don't know what the planned 15% will change about it, we'll see later).
The amount of DU is adequate in my option, it just doesn't fit the difficulty anymore.
The RNG on this map seems a bit screwed up as well since I get 1-2 trans and crappy myth from wave 7-20 and after wave 20 transcendent, surpreme, ultimate and 300-stat-myth items start dropping like mad (5-15 per wave). I was hoping for something around Mistymire survival difficult, or between Mistymire and The Summit. That would be a nice stepping stone into NM.
This is about what I had in mind with a stepping stone into high-stat-nightmare.
EDIT: I don't think it should be lowered to the difficulty we had before, because I was able to afk the combat phases on survial waves 20-30, which is far to easy, considering the good amount of trans, surp, and ultimate.
Oh and btw. through the 12 Survival runs I did at the old difficulty, I got only two upgrades to my armor at all (none for my 1200/2900/800/2700 Countess though).