Benefits to all sizes and variation is good. 29" works best for me personally 90% of the time but I accept others feel differently.
Some tech is pretty pointless, some is developed out of different fads. Wouldn't say boost is necessary for stiffness but after fat bikes showed that big tyres could be fun the standard tyre size has increased (rendering fat almost redundant) so boost makes it easier to fit bigger tyres. Gone are the days of struggling to fit 2.2" rubber between the chain stays.
Things move on and our old retro bikes (certainly pre 95ish) have more in common with gravel or hybrid bikes than what is considered a standard MTB these days.