Even with the tweak/nerf of the djinn's power, they have pretty much ruined any hope of soloing the harder challenges and maps on nightmare hardcore mode.
When soloing, you can't leave a builder in during the combat phase which means that every defense they zap cannot be rebuilt until/unless you win the round. Even if you do try to use your "builder" for combat, that only works if you have a build layout using one classes towers. If you mix and match, you can only rebuild the defenses of whatever class you have in at the time while solo.
Additionally, Trendy made the decision to retroactively add the djinn to the pre-existing maps which means that virtually every build layout will have to be redone and tuned again. I've already gone through that once when they nerfed apprentice towers in a big way a few months ago. Having to come up with new builds all over again on all of the old content is just tedious to me at this point.
A case in point is the Uber Monster Fest challenge. Prior to djinn, I had a build I used to consistently solo UMF. Now, I lose between waves 10 and 12 every time. Since anti-air defenses don't prioritize djinn as targets and I play a melee as my DPS/combat character, I have no way of stopping the djinn from unsummoning my defenses while they hide behind the tide of other monsters which rush closer to the barriers. There's nothing I can really add or change on my build layout that will solve that problem that wouldn't fatally weaken my defenses in other ways.
As it stands, if I want to continue soloing this, I'll have to bench the barbarian and play a ranged dps class and/or find a build layout with apprentice towers that works better. Both options would require me to spend significant amounts of time grinding out new gear and mana to upgrade said gear just to be able to beat content that I could previously beat without much trouble.
I'm all for the *NEW* content having new challenges and being even harder but I don't much care for changes to the game that completely change the nature of the previous content and make it orders of magnitude harder than it has been for a long time.