50 monster spawn and 10 years of evolution plus PK's rebalancing mod are enough to threaten Marloss Man Reborn. I have almost died a few times, the Solar Roller has been completely wrecked like six times, and MMR is approaching 100,000 kills.
I've always found it a lot harder to have less monsters and less items, for some reason. Sure, monster evolution can get pretty bad, but a halfway healthy character hopped up on Adderall with an entrenching tool and a Five-Seven if it gets really bad has always been enough for me to handle entire hordes.
When you fight three zombies a day and can't get anything out of cities anyways, can't find that Adderall or that Five-Seven or even that goddamn entrenching tool, when it's you and the skills you start with and the clothes you start with and a heavy stick or a makeshift crowbar living out a lonely existence with scarce resources and little to hunt, that's always harder for me. And a little more fulfilling. Though normal worlds with normal monster and item spawns can be fun too.