So I had a fight with four level 4 Redcaps in the swamp. Apparently Larian took their values pretty much exactly out of the DnD rules without adapting. That said if you look up the rules an encounter with 4 Redcaps with a party of 4 is considered deadly up to a level of 6 starting getting hard at level 7 (EA has a level cap of 4). And it isn't hard to guess why:

- Multi Attack that allows 3 consecutive hits
- Ironbound Pursuit that targets Dex Save and does 3d10+4 damage (honestly at level 3-4 ?!) => could one shot your characters if hit and good damage roll

And since it didn't seem to be challenging enough Larian added the swamp debuffs. I am actually pretty curios why Larian chose to make that encounter that way since it is obviously balanced very badly.

Since it is more or less an optional fight you could also easily miss it so maybe they wanted to see how player get along in a rather difficult/unfair fight.

But honestly I am worried it is something else:
They bloated up the HP of their other enemies and thought "Oh look the redcaps have the same HP as our other enemies in the game at that level (after HP bloat) so why not taking them unmodified!" (completely ignoring that their stats and skills are far too strong for that level). The fact that they label them with level 4 when you examine them points very strongly to that suspicion...