Drezen on core is quite fine as it is. If anything, I feel they even toned it down compared to the Alpha and first Beta. For example, the named demon in the tavern was a major pain in the ass, but is much easier to kill right now, same for the interior where a couple of fights are also easier now and I suspect that by release time overall difficulty of the area will drop even further. Also, now in Beta 3 you can assign someone to fight corruption while resting which was not possible previously, giving you even more rests until you need to activate a relic and there are 2 of those outside anyway so this translates to about 6 safe rests before you even enter the citadel.
The party I most often cleared Drezen with was this: Seelah Paladin 2/Dirge Bard 7, Regill Armiger 5/Hellknight 4, Cam-Cam Spirit Hunter 9, Sosiel Cleric 9, Lann Zen Archer 2/ Drovier 7 with Leopard pet with Bully for trip and the MC Rogue 1/Sorc 4/Arcane Trickster 4. Perhaps not the best party, but they did fine multiple times.
In terms of buffs, for this area, I just keep Heroism up since it's 10 min/level along with Greater Magic Weapon, Barkskin and Magic Vestment, Armor and, depending on how well I'm doing in a fight, start putting up others with shorter duration. Bard also helps with Inspire Courage as Seelah has enough performances to keep it up most of the time with Lingering Performance.
Overall, stat bloat or not, it's perfectly doable without optimal builds or tactics and, unfortunately, if you get filtered by it, you'll have a bad time in ch.3