Why change the core system so much? There is no need.
Just use monsters across the board with lower CR.
12 instead of 14 AC? 10% higher chance to hit.
Saving throws of 4 instead of 6? Same as having DC 2 points higher.
If you want to have faster fights/more hits, just decrease difficulty of encounters aka CR and viola, same effect.
So why change a system that already works? DnD 5e RAW has solutions for your suggestions without the need to alter the rules. So why change it?
My guess is to encourage advantages like height and backstab. Using height and backstab trivializes hit chances.
