Upon trying to complete all encounters on Hardcore i have noticed that Salan added debuffs to some of the T0 bosses that they did not have before, thus making them WAY overtuned.
So when he changed them to be level 115 he also seems to have either increase the debuffs effect or aded new ones that were not there before, which makes them way harder.
Most bosses in Derinkuyu are just bosses you can kill easily by either nuking them and facetank or just kite them slowly like Golsmag (he does have high dmg so i always kite him if its on a character with low gear).
Most difficult ones are:
Kite: Most difficult boss in Derinkuyu, has 5 debuffs that wrecks face and actually debuffs your character harder than the Darkness Falls zone Debuff (that alone should tell you how broken he is)
Kane: Has a debuff for -15-35% Damage reduction and Block, seems to only debuff you by 15% if you manage to "block" the debuff, which is strange. 2nd hardest Boss in Derinkuyu simply because hes on your ass 24/7 same as Kite and they both have high movespeed, so keeping out of range is almost impossible, especially since they have -movespeed debuffs on you.
It is quite strange since the other 3 Dragon Riders are much more balanced and Mandark for example is the easiest shit ever, he does NOTHING, while Laeroth requires you to move out of ground AoE to survive. Tarnitha is in my opinion the most balanced boss in Derinkuyu for T0 as she has a moderate debuff (Howl from her summonable pet) and does decent damage to your character (But not enough to rape you in seconds like Kite, and to some extent Kane) and her pets also doesnt SPAM the debuffs like Kite and Kane does, you will almost never be without the Damage reduction debuffs vs. Kite and Kane since they recast it so often.
I find it very strange that there are -damage reduction debuffs in Derinkuyu since it is the first raid and should be a means to get prepared for Darkness Falls.