There's a large amount of debate over this issue. Whatever your opinion may be, the study doesn't seem to agree with it:
https://jamanetwork.com/journals/jamanetworkopen/fullarticle...
Look at the chart for number of sexual partners reported by men and women by year. Honestly just read the study. It has data on many of the issues people are speculating about, including porn and what not.
If you were to believe that a small number of men are getting all of the sex at the expense of women, you would expect it to take a more bimodal shape with much fewer men getting 1 partner, some more getting 3+ and more getting 0. Instead we see the number of men getting 3+ declining over time and a big shift from 1 to 0.
Another important insight is that the rates of getting no sex drop significantly once you're a little older. Compare the 18-24 year olds to the 25-34 year olds to older. Looks like 25% drops down to 15% drops down to 5% in the most recent year.
Thinking of the male people I know who didn't get sex during college, it was mostly because they were busy doing other things or insecure.
It's entirely possible for women to favor only the top few men on dating sites but for this not to control the narrative of who gets sex and who doesn't. I'd go as far as to say it's likely it does not.