I wonder who are those wrestlers with no ground game that you say were great ground-and-pounders. Particularly talking about American wrestlers from back in the day, given that they coined the term "GnP".
Its common for American wrestlers to follow that model. Many of the guys I trained with were like that--a lot of wrestlers are averse to training Brazilian jiu jitsu or submission grappling and would just rather focus on learning to strike on the feet and pounding on an opponent on the ground. American scholastic wrestling, even more than freestyle, emphasizes ground control, what with riding time in college and unlimited mat time in high school. So coming out of folkstyle wrestling, most wrestlers are going to naturally have a sense of pressuring and controlling someone from the top. And that's without mastering the broader skill sets of submission grappling or Brazilian jiu jitsu, involving guard passing, guard retention, submissions, etc.
And that's largely in response to your comment that it was a contradiction to say someone was lacking in their ground game but was good or great at ground-and-pound. They are good in a narrow sense, specific to a certain skill-set that can be employed on the ground, but not necessarily good at a number of other areas of ground fighting or grappling. Although there is a sense in which every folkstyle wrestler that knows how to employ his skills as a good ground game. But its going to be narrow in a sense.
But as far as wrestlers who were good at ground and pound without having an exceptional ground game otherwise...? Coleman, Severn (Severn beat the crap out of a number of successful BJJ guys, including someone named Don Richards who was a big name in the Michigan jiu jitsu circuit but also did very well nationally), Tito Ortiz, Mark Kerr was great and ground and pound but obviously you can't question that he had a world-class ground game given his utter domination at Abu Dhabi. I think Coleman would have done great in grappling competition as well, honestly. Kevin Randleman had ferocious ground and pound, so did Quinton Jackson, Dan Henderson...Kenny Monday was able to show some very strong ground and pound in his single MMA outing against John Lewis who is known for his ground game.
I think we primarily have a semantic difference though, in how we are defining ground and pound. I think a lot of wrestlers are great in certain aspects of the ground game, where there are allowed to employ strikes, especially, without necessarily being good at the ground game or at grappling in a broader sense. I also think, in terms of damage, you should evaluate how well people were able to maximize their time on top to inflict damage on their opponent or to effect the fight's outcome. Whether or not its the sole criteria, I think it should have some weight. Gomi, for example, was able take full advantage of the time he had the great Hayato Sakurai in back mount, likewise for Sakurai's Team Ibaraki mates Ishida and Kawajiri. He also, when at the peak of his powers, able to control a world-class or at least very high level grappler in Ryan Bow ( Ryan Bow is older than me by a few years and he was still able to dominate both the Advanced, Senior and Open division at a Naga a couple years back) and a bonafide world class grappler in Chris Brennan using his grappling, wrestling and ground and pound. And of course, you have his performances against Rumina Sato and Mishima, both awesome grapplers and actually, able wrestlers as well. In terms of Kid Yamamoto, I'm thinking of what he did to Katsuda in particular, but generally, in his prime, he was a scary man from the top.
I would argue Kawajiri or Okami's greatness at controlling and dealing out damage from the top. In Okami's case though, I feel like if I was going to say specifically that he was the best Japanese ground-and-pounder all-time, across weights, I'd have to have seem performances where opponents wilted underneath the onslaught of his ground and pound in the same way that they did beneath the fists of Gomi, Kawajiri or Kid. If you're talking about just controlling an opponent, I think Miyata, at the peak of his powers, was as good as anyone. To me that is entering into a broader category. Kawajiri and Miyata, for example, are major submission threats, as Gomi once was and as Okami has always been, even if he doesn't pursue them as often. None of these guys would have been stymied underneath a green Joe Warren the same way Kid was and all these guys have shown in high-level no-gi competition that they are nothing to mess with (though again, to be fair to Kid, he did win that Contenders television tournament, rightfully or not).
I don't know, though, I really think this is mostly a semantic difference. I might be overrating Kid's ground and pound though, even in the narrow sense, admittedly. There was a lot of hype around Kid back when I was watching MMA all the time and his TKO of Katsuda always struck me as particularly frightening.
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