Many caves remain without light for players due to inaccessibility. 

What we see: many caves without light and many mobs, many lags

What should happen: normal more accessible caves and gorges, which do not have to be searched with x ray and illuminated in order to reduce the load from mobs appearing in the dark.

The screenshot shows not the worst gap in the ground, but more often than not, everything is much worse.

Playing on peaceful have less lag and less fps drops.