Games finishing at 2.5 or less item completion, and with the average level being ~12-15 has been way too common since forever.
To make shorter games fun, they need to feel complete, which means more consistency hitting the phase where players have a majority of their items and hit max level, and less hard snowballing (more back and forth; IE: Objectives become easier to take for the behind team, without taking away from the ahead team's ability to push. Something like turret HP being modified based on the team's comparative average levels or something. HoTS does it with an ammo system and no tower aggro on players if there are minions in range + destructible walls to provide protection rather than just the tower damage).
Also, items need to be toned down; it's fine for them to be strong, but 1 item more than doubling a champion's damage output or defense, and a full build putting up to ~95% of a character's damage output or EHP into items is ridiculous.
Ideally, damage should never reach the point where 1-shotting another player is possible, because that completely negates squishy melee heroes that don't have absurdly powerful burst/escape mechanics, but, as the game is, and has been for a long time, damage oriented heroes can hit a point where they can 1-combo someone building full defense if they are ahead, because of compound item efficiency (Which really should be the reverse, as it is in other games; completed items already have the advantage of only taking up only one slot; combining that with more gold efficiency just puts people that are ahead in an even more dominant position, as this last update has made more blatant, and it's an issue that can shut out people that fall even a little bit behind in lane almost entirely, depending on what champion they are playing).
and 
or 
. Also increase experience gain, not just gold.
There are things in this game that are called "late game Champions/items." You cannot force the game to be faster without leaving half of it completely in nowhere territory.
I'm pretty sure the point of "lane bullies" was to carry game early but falling flat late. And the purpose of late game champions was to carry the game late. No mystery. No doubts. When a lane bully was also too good late, is that something was not alright with that Champion.
But now we have a meta in which lane bullies lead you to Victory in 15-20 minutes.