This mission is not a thief mission, not really. This mission is a FPS game, with stealth elements. I say this, as one of the objectives is literally "kill every undead" and you can't really do that without a few swordfights.

You also have a big magic sword to help you in this task.

Honestly, design wise, this mission is fine. It's nothing special, very primative, but it works. You have room to sneak around, you can backstab some of your enemies, and loot is well hidden, but there is enough of it to not get frustrating.
The only real issue is that the primary objective, requires you to pick up a corpse, with no defining way to tell which corpse until you pick the right one. Usually the "locate a corpse" objectives tick as soon as you find the corpse, with a voiceline or similar from Garrett, or when reading a book or scroll next to said corpse.

Still, ultimately, this level isn't that bad, it's just it is a combat focused level, and most people won't be looking for that from thief.