The only downside is that the participants need to be familiar enough with their chosen game to do a randomizer which means roping in casual players is difficult.

Casual players can be fine with some games. Some actually become easier with Archipelago (e.g. Noita, Risk of Rain 2) since you’re getting meta-progression between runs that normally wouldn’t be there. Others though are especially punishing for new players (Doom comes to mind - you have to be pretty intimately familiar with the levels. There’s keys hidden in secret areas sometimes, for example, and ammo can be very scarce.)