The 4 div comp has a lot of logic to it. You play everyone twice. Shorter season to reduce fatigue and help hold players at lower level team due to mental fatigue. Relegation and promotion will still help balance the better and worse of each level.
The worst of div 2 this year would have struggled against the best of div 3 so it might also help close that gap.
The worst of div 2 this year would have struggled against the best of div 3 so it might also help close that gap.