So it turns out running Duty Support of current-level dungeons gets me about as much XP, as quickly, as running basically any Duty Roulette, when running my RDM. Would be VERY different as Tank/Heals, nevertheless.
Aside from Trials, Roulettes are invariably slower due to DPS queue times and chance player DCs/delays/etc, and the bonus daily XP isn't enough to warrant the time waiting, sadly. At least, not in my experience on my world/data center (Sophia:Materia). The time taken to actually run a duty roulette on top of queue times (and, even w/ XP buffs, the risk of having to run fucking Praetorium again), might gain me a better XP-per-hour rate, but not enough that it's worth all the downtime for me.
I can slam out about 2 DS's an hour (depending on the dungeon ofc, sometimes maybe 3), which, at least at the early stages of RDM, is enough for a level per hour, which is faster than just about anything else atm, AND I'm not bothering anyone if I need to AFK for 5 or idle out or what-have-you.
Hopefully Heaven On High is a bit more... Solo friendly? Than PotD is for me (at least, at low aetherpools.)
Really enjoying RDM tho, esp. now that I have Vercure. It's not as strong as I'd like, but the freedom of dropping a dual/swiftcast on a heal (which I have mouseover for!) is divine, and is exactly the versatility of the Enhancement Shaman ala WoW that I love. Hotbar organisation is still... An ever-shifting nightmare for me, but I'm getting some muscle memory.
Maybe I should consider a free company.
But I've had an abysmal track record with staying active in guilds in the past. Hm.