I see no reason to think it isn't wide spread. In fact, I'd say the lack of awareness itself is proof that it is widespread.
If a person has a PMO habit (and effectively has PIED) before he has any sort of sexual encounter, and in many cases before even hitting puberty, what is his frame of reference of how his johnny is supposed to work? The fact that people aren't scratching their heads about this more indicates to me that it is more common, not less. If it only happened to, say, 2-5% of the population, then they'd hear enough from friends or sexual partners to cue them in to knowing that something is up. But if everyone else is seeing the same "problem" it may not seem like a problem at all. There isn't much of a way of checking across generations, either, unless some guy were to ask his dad "papa, what were your erections like when you met mom?". Women these days are as confused as men. They're likely to think that losing an erection after a minute or two and having to do all sorts of things to keep stimulation up is normal.
So, what is the real percentage? I have no idea, but my guess is that among people who are sexually active enough where comparison is going to happen, heavy porn use is probably 80%-90% or higher. The reason I narrow it down to people who are "sexually active enough" is because they'd be the only ones who had encounters with PIED and a "control group", sexual experiences untouched by porn and PIED.
On one hand, a couple that waits for marriage to have sex and thus each has only ever had one sexual partner and probably doesn't talk to friends out how their sex life goes will have no frame of reference. On the other hand, how many people who are actively involved in hookups and have had multiple sexual partners are also saying no to porn? (Exempt people who have had porn addictions and then quit, they're the ones sounding the bell anyway) I'm sure they're out there, but I've never met anyone under 40 who is an advocate of hookups and casual sex but is against porn. They'd be the unicorns that would be able to spot the real difference. I know that this is a false binary of sexual practices, but I hope you'll see my point: the people most likely to have enough data in front of them to determine "normal" are getting skewed results from porn use, and the fact that no disparities are showing up in these discussions shows to me that the consequences of porn usage are present in the vast majority of cases.
Whenever a society's health metrics move in unison in any direction, changes become far less noticeable. Whenever I watch an old movie, I'm often taken aback by how skinny everyone looks. Then, some character will be called "fatso" and they don't look nearly large enough for anyone to take notice today; take a look at guys like Edward G. Robinson or Fats Waller. But, we can't know what sex was like for prior generations that easily... unless someone wants to ask their dad.
