I'm surprised you're finding them hard to fill tbh.
I also view them as a fun romp to celebrate the regaining of my Epic Destiny powers.
Just make sure your lfm level range is upto 21, they're on Elite and you don't wait for a full group to start. Jump in with a hire, "fun/favour/xp bb" lfm and I'd be stunned if you weren't full by the time you were 10mins in.
The Epic kids will undoubtedly do the lion's share of devil busting but myeh.