So we’re all aware of the uneven matches that are likely to happen when solo queuing for a single match tourney.
My suggestion is why not just make them like hot-joins? You can come and go as you please. That way if you have people leave/never join you can get an actual 5v5 going and the team with less players at least has a chance. It’s not like tourney’s are actually some end-all-be-all measure of skill and pro-leet-e-sportsiness (as much as people want them to be). Just treat them like hotjoins and make sure the matches are always fair.