Can relate to a ton of this. The first thing I ever type when joining a group is that I'm in team voice if people want to join. And if I'm queued with a group the first thing we do is switch over and then say the same thing. Results are about 50/50 I would say, with this leading to half the groups I'm in having actual real, helpful communication and half of the groups with people just ignoring the request. Whatever.
The hero complaints arent ever going to go away and I always just try and be nice. Like, "hey, I don't want to tell you what to play and if you're best with Sym here whatever but she doesn't make a ton of sense on this defense point." Or something like that. I'd say I strike out more times than not, but sometimes people switch. I can't place blame though. On offense I'm playing Soldier or Lucio and not much else.