Yeah, I guess stability is an issue as well. Honestly, 4v4 just feels pretty bad so far. Rarely do people communicate, and matchmaking is pretty gung ho with the skill levels of those involved.
If you 've just started 4v4 then your rank will be low and you'll be teamed with terrible people.
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Of course this means if they do drop or quit its no great loss, especially as how the opposition tend to get complacent when that happens.
However 4v4 is not for everybody, and arranged 4v4 and random 4v4 are different beasts.
Random 4v4 is all about dealing with the chaos, you have 7 people to worry about and not all of them are the enemy