The problem isn't game length
It is when games are decided. I still have plenty of 30-50 minute slug fests. The problem was that the winner was decided by 10 minutes. Just, unlike pros, low tier players cannot see it and don't 'open mid'. So they drag it out for another hour. The problem isn't how long the games actually last. It is that the winner is decided so early, with a 72% win rate for whomever kills the first tower, the winner is essentially decided within ten minutes most games.