When I was a young boy, it hurt like hell to wash the glans in bath.
Sometime between age 5 and 10, the glans lost sensitibvity such that by age 10, it had become pleasurable (wink wink , nudge nudge).
By the time I was about 14, I recall a summer where I tried to keep my foreskin back in underwear as much as I could. Stopped when friends told me to stop reaching into my pants (I would go in to retract wheever I felt foreskin going back over head.).
After I became semi cut, I strived to keep foreskin over head in underwear, but every erection required it retract so glans stayed exposed during nocturnal erections. In 2004, one specific event saw me in loose underwear and foreskin rertracted and I realised it felt comfortable and pleasant and was able to prevent erection. That started the final push to get a full circ.
As it turns out, once fully cut, I saw little to no change and I was I comfortable in underwear from day 1. (though I still generally wear tight fitting underwear as in loose underwear, i am "distracted" by the nice sensation.
Now consider somone is is 20-something and had phimosis all his life and never saw his glans. His glans is likely to still be like mine was as young boy, so after circumcision, the glans will adapt big time to and adult's glans. So he will notice a huge change in his glans.
But someone who has retractable foreksin, especial;ly if it self retracts during erections would likely see far little change in the glans.
Also, one must differentiate betwene loss of sensitivity and a gain in erection control. Just because you get used to glans in underwear doesn't necessarily mean it is less sensitive, it just means yor brain has learned to control the sensations. Cirucmcision does not change nerve endings on glans.
