is the way the numbers and analytics say.

Efficient offense does two things—get open looks from three (especially the corner) and get open dunks and layups, usually as a result of shooting the three well but also with well designed cuts and passes. The efficiency is based on the expected value of different types of shots—I.e. points when shot made times percentage at which you can make the shot. Layups and dunks go in at about 70% if not too contested—they are worth 1.4 points each.
Open threes should go in at 35-40% expected value is 1.1-1.2 points per shot.

Even the very best post guys do not generate points efficiently in the post up game compared to open threes or dunks/layups where guys get downhill. A good one will get it to go 50% of the time and it takes a long time to do. It is not that it can never be used but it isn’t a sensible basis for an offense unless that’s the best available for a particular team (or game, say if threes simply won’t drop).