First of all, Xbox or PS4? I mean your son.
Also, to address your point about lack of groups, there are a number of LFG sites that are quite active. I’m sure if you are high enough level, people would love to join a session for Last Wish or whatever it is you want to complete.
Same for Gambit. It’s much easier playing with mics, and you’ll frequently get good players on both sides of the playing spectrum (PVE and PVP).
Gambit is the most rage inducing thing in the world. Whenever I run with randoms, I always get teammates who don’t care if you die and just go pick up notes anyway. Other times there are people who are saving up for a Large Blocker when the bank is literally 2 motes from being full. Then there is the crowd surfer who doesn’t seem to understand that PVE enemies can actually melt in this mode, even the low tier trash mobs.
Surprisingly enough, I have a decent win record for Gambit.