New players, and premades trolling, griefing, smurfing, boosting or whatever they want to call it is by far the 2 most devastating factors atm.
Seperating premades and solo-Q'ers should be the first easy step.
Blizzard should then really use levels aswell as a factor in their match-making.
New players are consistenly causing this "ELO Hell"-problem to be as huge as it is, due to them exiting so high from placements.
The main problem is that new players almost always insist on playing dps heroes, most often also poorly chosen ones.
The ones with really high lower skill cap, that requires a really good aim to be efficient with.
DPS heroes are the ones to supposed to bring the damage, kills, or counterpreasure on the other team.
When DPS heroes on your team are the weakest link, you are almost guaranteed a loss.
Learning to play tank and healer firstly is a much better idea, and is often more forgiving (or easy) to play for the team.