It is not fun to anyone involved. Just stop. Everytime I have to friend the premade and wait for them to get in a match so I can queue and try to have a fair match.
The fact that people can duo queue in a 3v3 set-up is pretty ridiculous in general.
The problem is: In 5 vs. 5 conquest in ranked you can only duo queue at max. And while the mini season is "ranked" only ... the 3 vs. 3 ... the fact that they allow 1-3 queuing also shows that the mini season is only meant "for fun".
I recommend to early surrender (rush to the enemy and quickly let them kill you) to save time if in ther 1st or 2nd round you noticed that the other team is much more coordinated. Mini season is only about getting the season reward chests and achievements as conveniently as possible. (After that: Unranked 5 vs. 5 until the ranked has 5 vs. 5 again in the normla season.)
Actually it should be the other way round. 3 vs. 3 and 2 vs. 2 only allowing solo queuing. More people in queue in a 5 vs. 5.