That's because the undermountain enemies are meant for level 7 characters. As well as the rift.
When I last checked, both areas were level 6.
I was in the Rift when the maximum level was 5. In general, I did not experience any particular problems.
However, this was in the early versions of 0.3 with their non-nerfed crits where I could sweep out the whole party of enemies with one good hit of the spell.
Undermountain, it seems, is also a quite possible location for level 5, this is more a matter of tactics and manual control than stats.
Some opponents, however, are more problematic than others. I find the Jotuns (Rift) and Earth Elemental (Undermountain) quite frustrating opponents, I don't like their damage at all. I haven’t seen Jotuns for a long time, so I don’t remember exactly their damage, but the Earth Elemental is able to kill with two hits and attacks
three times per turn...
Okay, let's forget about the Earth Elemental, my battles with it do not always go as I would like, but at least I worked out tactics and, with luck, I win in two turns. But I still cannot develop a reliable tactics for Jotuns, because I refuse to consider such a tactic to use Banishment on one and the quick elimination of the other.
Excuse me for asking then, but why then haven't they raised the level-cap? It seems kinda silly to keep releasing content that the players aren't actually equipped to deal with.
In fact, the current opponents do not exceed the level cap in terms of level. Use "Sense" in battle and click on the three dots under the enemy status slots, there will be a level indicator and other interesting things.
As for the Level Cap, it's about gameplay and game balance. The game is only half ready and taking into account the planned maximum level of 10, the opponents of this arc should be 6-7 levels.
The current level cap allows debelopers to balance enemies exactly at the same level characters, not superior.
It also gives developers more time to come up with new perks and powers. Just for reference: the opponents in the Rift (at least the old ones, it is possible that new ones I did not know) do not have level 6 powers, since by that time these powers had not yet been invented/balanced.
P.S. Personally, my problem with opponents is the difficult acceptance of the fact that opponents can have multiple action points and are not bound by the five slots for powers. I am also pissed off by this bullshitium-made Frenzy that constantly negates already unforgivably short-lived debuffs....