There is scaling, if you and the other player are actually close(ish) together, though my understanding is that it's still easier with others than by yourself. I've only played solo myself though, so just answering based on what I've read.

I started playing about a week ago, and have just gotten to the swamp biome myself as of a day and half ago, and all I can tell you, is it gets easier. Yesterday evening I upgraded to an iron buckler and iron mace with what Iron I've gathered so far and the swamp this morning is SO MUCH easier, with just those two upgrades.

Also, regarding your spawn rate thing, are you staying close to the edge of swamps? There's a 'thing' in the game related to being on biome borders where you get more spawns because of 'border guards', basically.
When I first ventured to the swamps I was too nervous to go farther in and noticed the same thing about constant spawns....it's actually easier if you go deeper in. Despite that seeming counter-intuitive.
The sunken crypts also can't appear at the biome edge, so that's another reason to go deeper in.