I'm pretty sure you have the same chance for getting stuff playing with your friends as with random people or to some degree solo ( lower due to no mf ).
I tend to play alot of all 3, when I play solo I rarely find anything special, with friends rarely anything special and likewise in public grps. Sometimes though, I just get lucky and get 10 legs in 5 mins. It's rng really, but our minds plays a trick on us if we do something and something happens, we quickly conclude that they will be linked. Like leaving a grp of friends, joining a public and getting some goods legs.
If you are really concerned about this, try to make large sample sizes rather than basing this on single events, those prove nothing.
@OP: I had a similar feeling, playing with 2 friends they always got 4+ legs a rift whereas I was lucky to get more than 2. This went on for some rifts, maybe 7 and I started to come up with the same theories as you. But as we continued playing it started evening out, I remember a rift where they both got 1 and I 7.
It's all rng, but it can be hard to see it in small sample sizses.