My friend's GF runs with us occasionally and even though we are on PC, we usually just keep chat set to group instead of whole team.
When I'm playing solo I team chat by default. I have many many years of MMO gaming under my belt and I am not shy about using my mic when it is needed. In my experience, most people, especially in competitive play, want to win and are reasonable about how to go about it.
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Another data point to throw out there. I just had a competitive match as Zen. We defended the 1st point on King's Row and they never took it and then proceeded to blow them off of the 1st point on our attack turn to win the game quickly so I am not sure how that skews things. (Total game time was just over 7 minutes)
11 elims, 3 deaths, 4100+ dmg 4900+ heals, 2 gold medals and 1 bronze. The win netted me exactly half a level worth of exp. I don't know if that's good, bad or average, but there it is.