First of all:
In the Public Test Version there was a bug that the mistland raid-events did not spawn enemies. And there was a bug that night spawns also spawned at day and did not despawn anymore. So a lot of old "Mistlands is impossible to play" comments are from these times.

Within the official Mistlands Release these Bugs were fixed. The Mistlands raid-Event now worked and was indeed brutal!

A Week later IG changed the Mistlands Raids so it does not spawn in the Meadows anymore and they reduced the amout of enemies in this raids.

So your Base in the Meadows is Seekers/Gjall-safe now!

https://valheim.fandom.com/wiki/Events

"army_gjall" - Raid only occurs in the Mistlands
"army_seekers" - Raid occurs in Black Forest, Plains, Mistlands, Ashlands, Deep North