This is going to be a very, odd… way to look at things for many people, but, it should be a way people who have developed games will understand.
Balance the 3 roles, so you have roughly the right amount of people playing each role.
I’d remove priQueue so it is obvious what is going on, and so you can get better games coming out of it.
Then balance for player retention for the 3 roles, on a percentile basis. So you don’t have one queue blow out.
It is a VERY practical way of doing this.
After all, if you lose your tank/support players at the current rates, PriQueue can’t save you long term.
You have a game which relies on a healthy mix, so, balance for that mix.
Anything else means you lose the DPS players anyway. - as you have to trade queue times for match quality at increasingly worse ratios.
Either DPS players leave because match quality is garbage, or that the queue times get so bad you can’t sustain it.
OW2 is going to have a PvE mode, and you HAVE to know that the Support / Tank players are more likely to play it than DPS. If they were about fragging other players, they wouldn’t be supporting or tanking.
So, you will lose a bunch there, and if you are already having to sacrifice match quality to make up losing them faster than DPS, PvP will suffer hard, and you won’t have many places to go.
Trying 3 DPS / 1 Tank will work for a while, but like priQueue it will come to it’s limits as well.
PvP is important, please don’t throw it away.