I suggest adding some kind of middle tier, a veteran dungeon, between normal and high roller/ranked
https://darkanddarker.featureupvote.com/suggestions/492036/make-3-tiers-of-dungeon-normalveteranhigh-roller
The Idea:
3 tiers of dungeon might bring a bit more balance to lobbys and to the risk/reward for players:
the first tier, which would be what is now normal, would be aimed at people in grey green, players that start or casuals that do not have an economy and want to build themselves a basic kit, with a slightly lower drop rate regarding blue purple + items (maybe more green items then though) to push geared players out.
The second tier, "veteran" difficulty, which would have a higher drop rate (something in between the current normal and high roller) and more red monsters with an occasional nightmare monster. it would be aimed at players with green blue kits
The third which would be the current high roller, that leaderboard is based on. It would be aimed at blue-purple and above kitted guys and those who want to have a go at the leaderboards.
Why:
Currently a lot of average to good players that are correctly geared do not go into high roller as they know they will just get 1-2 tapped by overgeared teams going for the leaderboards (or risk losing gear to a dc but that's another issue).
These geared players in turn stomp players that are in normal as they don't have an economy or just lost all their gear.
(Yes git gud i know, but sometimes you have a bad session, you lose all your gear and it feels almost impossible to gear yourself back up as you get destroyed by gigachadgears every couple of games and the latest swarm update often makes you cross a large part of the map which gives you less time to loot, that or you start in the finish zone).
The system i suggest could also make the "level matchmpools" irrelevant.
Players could still queue any mode they want but there would be no use for a geared team to stay in normal killing grey players.