I think the auto-adjusting world tier was almost perfectly balanced for two skilled players with complementary builds going through in coop. There were wipes, and therefore tactics and strategies, so things were great. A couple of weird spikes here and there but nothing we didn’t get through without getting so exacerbated as to lower the WT. Other than in one exceptional circumstance when a crash during a boss fight coupled with the inability to join a game with a boss fight in progress meant we each lowered it for the purposes of essentially skipping it.
My co-op partner is busy now some I’m rolling out solo on expeditions. I’m managing challenge tier 11 golds reasonably comfortably, but this is a coop experience at its heart. I find the inability to self-revive in solo play bizarre. You get to do this once in coop, per ‘arena’. Fairness would suggest you should get to do this twice when solo. Perhaps with some additional time penalties in expeditions to keep things balanced.
I can’t help but feel that if you’re schlepping through this on your lonesome, you are missing out. Though perhaps if the matchmaking wasn’t so incompetently implemented I’d have a stronger argument there. The times I’ve tried it’s been too buggy to be worthwhile.