I finally hit Lv30 today and tried out the two Hard Daily missions. Got matched with all skilled players and steam-rolled right through. Decided to push my luck using MM for the Challenge mission, and.... yeah. Even with nobody using mics, we made it pretty far but as soon as we wiped once people started dropping. It wouldn't let me open the fire team to allow new players to be match made in, so the whole operation derailed.
Just one man's single experience but not exactly a pleasant one. I probably need to grind up better gear since I was getting destroyed but it was discouraging all the same.
Division will have a "gear score" in the game when they bring in incursions but for some reason it's not in the game yet. The difficulty of Challenging mode would be much more clear if they included the gear score. Massive really should have put a recommended gear score on the challenging modes.
You should really be 90K DPS/ 60 K health / 10-15K skill power or better to do a Challenging mode. I usually try to do challenging modes with a set group. That's one reason I'm afraid to jump into the PC master race (no friends) vs PS4 where thanks to destiny I have a massive friends list.
When your a fresh level 30 you don't yet have the gear to do a challenging mode. It's best to spend some time in the dark zone until you have full superior (purple) gear before attempting a challenging mode. You can also buy the Pakhan LMG at the Security wing vendor for around 500K credits, as that is a really good started High End weapon for challenging mode.
I think doing a Challenging mode as a fresh 30 with low equipment is like doing a 280 LL nightfall as a 220-240 LL. It get's a lot easier once you have better equipment.
As far as the four challenging missions currently in the game, you also choose a bad day to run the daily challenging mode. IMO in terms of difficulty levels 1-10 (1 being hardest and 10 being easiest)
1) Russian Consulate
3) Warrengate Power Plant
...
9) Lexington Event Center
9) Lincoln Tunnel
So if you try Lexington or Lincoln you'd probably have a much better experience. I would never try Russian or Warrengate without a set group myself.
I don't know how it works on PC but on PS4 you can open up your fireteam in the group management section to public, and then people will join very quickly via MM when somebody drops. Not sure if that was bugged for you or what was going on.