There could be separate queues, one for groups (of 2, 3 or 5 players) and one for solo players. That's what people've been hoping for for a long time, at least here in Brazil. On the other hand, I know this would split the playerbase and make queues longer, but it might be a price worth paying for better-quality matches. And perhaps it may actually even find mactches as fast or faster, since the solo queue wouldn't need to account for groups.
By design players can't be boosted on solo-only queue unless they are queueing at the same time and throwing if they get on opposite teams, which at the same time would probably result in them being reported frequently (this already happens, by the way).
Group-only queue matches would theorically be tougher and boosting could only go so far, unless it is 2 or 4 people boosting one, and even then there's a point were they'd start losing anyways, and that single player can't return to play alone and ruin matches later on, the boosters will have to carry the boostee around (no pun intended) as (s)he won't be accepted by other parties.
Alternatively, if queue times end up being a problem, Ranked mode could be group-only (2, 3 or 5); it is a team game after all, forming groups should be incentivized in as many ways as possible.
It also solves the problem of non-partied duos ("solo" duos) that throw if they are matched against each other. Could also strengthen smaller communities like Australia or SEA where queues usually take longer, or at least they could migrate to play on a different, more-populated server as a [laggy] team).
Forming groups even helps when it comes to reducing toxicity, people are less likely to be toxic in a group, if they keep being toxic they're more likely to lose focus and keep losing and the group would naturally dissolve.
If you are strictly a solo player you can always find a temporary duo or fit into a 4-man squad that's looking for the 5th player. This game does have an LFG channel after all, it could be improved and put to use. Or if you are dead serious about playing solo, team games are not for you just try hard on Casual.
Groups do have a few problems, like getting stuck playing a class you don't like every match because that's what's left, but then you can always politely ask to switch every few matches, or find a different party, or play a non-standard comp and own the responsibility over this choice as a group.
talk about overwatch, LFG, matches being harder AND FUCKING MATCHMAKING NOT MATCHING SILVERS WITH DIAMONDS.