Also been playing this over the last week or two and ran into the same issue as you. I used a slightly different setup with Rogue PC and War/Clr/Dru/Wiz party. Farmed the 700k demon in Krom Razz enough to get all the drops my party could use. Then was able to clear Sunken Temple outside of the summon event. I tried some other bosses like Cyclops and Pyroth (fire ele) but both melted my face at or before enrage with 13 vet points. I would guess that Sunken Temple is probably the next step, until all gear is acquired from there. I didn't do Vault of the Vanished either, so that might be another spot.
I was getting bored of the game at that point, so decided to try a warrior but no way I was going to get through leveling up another toon before quitting. So in grindy games, when I am close to quitting is when I usually cheat in order to get a few more hours out of it. I learned how to dupe items using cheat engine and auto-leveled up the warrior to match the rogue with all the same gear of the rogue's party (easier than transferting all the gear, if I wanted to jump back and forth between both toons). I used a party of CLR/WIZ/ROG/ROG in order to try to keep up with kill times for rogue PC, but still couldn't kill Cyclops and the demon in Krom Razz didn't seem any faster (it was actually a harder fight too).