So here are my thoughts on "long games".
We removed back dooring of towers (without minions) because towers were too weak...
We buffed towers durability because they were "falling too fast"...
We buffed baron, and dragon because they were "too easy to take"...
We removed tank's durability and traded it for CC and damage, because tanks were "too braindead"
You can have 2 of the 3.
Strong Champs, Strong towers, Strong objectives (baron dragon)
You cannot have all 3 without creating a longer game.
If you have strong champions and objectives, towers will seem weak.
If you have strong towers and champions, objectives will seem weak.
If you have strong towers and objectives champions will seem weak.
Just make pushing easier so that the losing team can't stall out the game. Then we can have strong champions+objectives. Hots doesn't have an issue with feeling tanky, and they have mostly 20 minute games.
Also, in response to your "Your games have respectable times". If you look, my longest games (bar a few) are losses. Do you know why my losses take longer? Because I know how to stall out a game. Something that has been lost mostly because of this high damage meta. Out of my last about 25-30 games only 4 that I won lasted 30 minutes or more.
If you look at the longest games they are all because the team wouldn't group/take towers, they wouldn't splitpush/take towers, or they just would try and fight 1v5. IF you want shorter games look at nerfing towers. They are very difficult for anyone that isn't an adc (or yorick level split push) to take down.