TBH I think the latest research says that overall, people circumcised later in life don't detect a difference in sexual quality (this is paraphrasing). But the mere design of such an experiment is flawed because you're asking people to recall and accurately compare function of tissue that doesn't exist anymore, and sex feels so rewarding for most, regardless of circumcision or not, that I don't think that this kind of research can really demonstrate much for these debates.
Uncircumcised men have lots of options with stimulating their penis. They can choose to use the foreskin or not. The foreskin itself is full of nerves that we can literally feel, and they feel great. These nerves alone can cause many to reach orgasm. And on top of that, the foreskin glides across the head of the penis, full of surface nerves that have not been desensitized from clothing and dryness, and both tissues involved feel really good.
So I can imagine that if circumcised, that foreskin tissue and feeling simply isn't there to feel with.
Does it mean sex is unenjoyable or dysfunctional for circumcised men? Not necessarily. Although I guess some circumcised men report difficulty reaching orgasm, especially sometimes in a condom, we all love sex and we all sexually stimulate ourselves, so even if you don't have a foreskin, sex is great.