You say you watched "tons of guides on Youtube" and yet leeches destroy your boat, blobs poison you and wraiths appear at night. There are multiple approaches to each of these "problems". Either you guys are not learning from your experience (you repeat the same mistakes, as we all sometimes do until we realize it) or you managed to find a swamp that is home to Bonemass -- those are known to have spawners galore as well as crypts.
Also, someone just posted how they are seeing an unusually high number of creatures around their bases. It could be a rare bug or just particularly unfortunate seed or rng. You could test it by finding another swamp; see if it behaves differently.

The only really hard time I had in my current run was when a 2-star Draugr archer had spawned the second before I destroyed a spawner inside a crypt. It took multiple runs to get my stuff back because he and another Draugr kept camping in the lobby. I still absolutely loved the challenge. It has been a few weeks and I still remember it fondly. :-)

If you have mastered the plains, like it sounds you did, swamp should be a piece of cake indeed.