QM matches only mirrors select roles, and doesn’t use fan-made rules people assert should be in place, but have otherwise not had any significant statical impact on game matching. ie what is “fair.”
“Specialists” were match as a ‘ranged assassin’ before, so your complaint about the ‘reclassification’ is pretty much bronze-lord levels of complaints where people are essentially arguing delusions because they’re just looking to complain, and not actually play the game. Matchmaking doesn’t account for a ‘lack’ of skill 
One side heavily favors diving on the enemy, the other side lacks reliable cc to stop that. If you were to search the forums, you’d find all sorts of topics that constantly assert they had ‘no chance’ against these sort of variations, not because they’re ‘unbeatable’ but because players don’t know how to play.
One side has lots of summons to act as a ‘temporary tank’ but otherwise has long cooldowns, so their contributions are reliant on the other side standing back and waiting.
Abathur is the ‘better’ hero for “healing” an unorganized team, but that side has delayed burst-heavy damage that could be mitigated with a decent medivh who’s doing more than just spamming an ability because it’s off cooldown.
Malth has ‘specialist’ levels of waveclear, mephisto is a ‘mage’ and has plenty of aoe, and Valla has ranged abilities and access to spell armor to mitigate most of the concerns from the other team. Everyone on that side can talent into suitable mitigation and self-sustain to hold their own when fighting on the objective.
Since you’re complaining about Quick Match, that means you’re playing on maps that have “Objectives” and “Mercenary camps”. These are tools that aid in controlling the game map to provide boons that might otherwise be lacking from non-‘specialists’. “Specialists” on the other hand, especially if stacked, are capable of ignoring the objective, but once an objective is claimed, that usually provides more clearing power than the specialists provide – which is generally why specialist-stacking is frowned upon, regulated to boogie-man stories, and doesn’t hold up in ‘average’ player experience. So the forum response falls into advise suited for low-level play where players are volatile, refuse to learn to play better, and just loop the same complaints for years on end.
The main issue is that one team favors afk-pushing and has an abathur hat to pick-off 1v2 fights while the other side breaks out into flame wars of blaming each other or matching since they spent all their years of complaining in one game after the next, so that’s the ‘skilled’ they learned.