A lot of players, including me, dislike DC and Tchort battle. For me, the whole location and the final combat feel unfinished, like there was supposed to be more content there, but it was cut. Another big problem, is that a build that was viable for the rest of the game may fail miserably in DC, and especially in the final battle.
So, I think Deep Caves and Tchort should be re-designed. Mind you, that does not mean "dumbed down". But consider the final combat: it seems that most players either can't beat it, or one-short Tchort, depending on their build! There is little middle ground, where fighting Tchort is hard, but enjoyable problem that depends on tactical skill and thinking, or maybe just hard work.
Here's what I would propose to do to fix problems with DC:
1) Clarify threat Tchort poses to Underrail. Six doesn't explain anything, and neither do Faceless or computer logs. They describe how the current situation in Deep Caves came to be, but after reading all materials I could find, I still do not understand why should I believe Six that I need to destroy Tchort, or what exact danger it poses. Until its own dialogue about eating souls, for all my character knows, Tchort might eat evil and defecate rainbows!
2) Add a way to make Faceless friendly even if you didn't done right by them before. After meeting with Six, your goal of destroying Tchort coincide with theirs. They should be able to put past animosity aside, after you prove yourself to them.
3) Add some dynamics to Tchortists/Faceless. Currently, both factions are nearly completely inert and exist mostly as decorations (if you befriend Faceless). Faceless do not even react to opening of gates to Tchort!
4) Trader should sell rifle barrels. It's laughable when you have a high-quality weapon frame, but no barrel in ANY of shelves! Also, maybe allow trade with Faceless for electronics?
5) Let player use either faction for the final battle:
a) For Faceless, help them wipe out Tchortists camp. Then, help them find a (very limited) number of devices that would let them withstand Tchort's psi-curses. Then, a (small) squad of Faceless will join you as meat shields during the final confrontation.
b) For Tchortists, help them drive out Faceless somehow (maybe an explosion at Arke Power Plant to collapse their caves?), then lead an attack on surviving Faceless. Then, help interrogate a prisoner, who tells them all about Tchort, how it is not a god, but an abomination. Faction leader kills prisoner, but a small number of Tchortists lose their religion and join you as meat shields during the final confrontation.
c) For players with very high Persuasion (or/AND Intimidation!), allow an options where BOTH factions help you, after you complete some very hard quest (possibly related to Monolith in worm caves)
6) Change location of final battle. Access to Mutagen tanks should be A BIT easier for non-stealth builds.
Other option: make every destroyed mutagen tank also lower respawn rate of Tchortlings, or switch off one of their types (one tank - no more Devourers, two tanks - no Sowers, three tanks - no Scanners, for example)
Other option: allow player to use Bio-gas grenades to stop Tentacles from respawning even without destroying mutagen tanks (for example, Tentacle will not respawn IF KILLED by damage from Gas; or Tentacle will no respawn while gas is around its death places).
Other option: at least, add a hiding place near north-east mutagen tank. Currently, it's the hardest one to destroy.
Other option: make tentacles always miss a turn when they move (currently, it seems to be random). It will make getting around the map a TINY bit easier, maybe saving some players.
After implementing such options, it is possible to make Tchort itself, or its tentacles a bit harder, though I don't think it would be necessary, but only playtesting will show.
Overall, for the design of the final battle, I urge developers to look to boss fight in Geneforge 5. It's quite similar, but way less unbalanced!