Not exactly sure what your angle is here tbh.
The obvious criteria for a counter striker is that he preferably counters in exchanges vs initiating them.
The most obvious cases are the strikers that move backwards, trying to lure the opponents in. The O'Malley's and Adesanya's.
In second line, as you're suggesting, there are guys who manage to do it while applying forward pressure.
That is only really successful though, as long as those guys have a credible weapon in close range. Islam's TD threat for example, even Yan's TD threat, or the inside boxing of someone like Topuria.
Sean is a bit of an odd one out here, because he literally just tricks guys into avoiding the infight with him at all cost.
His demeanor appears like he wants to get into a dirty boxing match, but that's not where his success comes at all. His frame allows for efficient striking in the pocket, but besides the advantages that his style brings naturally to that, he's not all that good when met in the middle. He wants to catch guys moving away. Or exhaust them by forcing them to throw at an uncomfortable volume, while being able to avoid any significant damage.
It's pretty good to see in the Imavov fight, as well as in the Abus fight. If guys stay in his face, he looks very beatable. His reactions look worse and there are all of a sudden actual openings.
A lot of guys just decide to move backwards vs opponents that move forward, while there is not always a good reason to do so.
Just some thoughts, but to come back to your question, in general guys have to be at least decent strikers overall while bringing to the table either very dangerous boxing in the pocket or a dangerous clinch or takedown threat. There aren't a whole lot of guys who are great strikers and great grapplers and there aren't a lot of guys who have the composure to close the distance without striking first either.
So naturally not a whole lot of fighters will qualify for that list. A lot of names have already been mentioned.
Guys like Ankalaev, Makhachev and Yan. The later Jon Jones kind of.
Guys like Oezdemir and Shavkat I suppose. They look less clinical, but they don't throw a whole lot first either.
On the cleaner striking side you have guys like Topuria, arguably Fiziev although he doesn't really put too much pressure forward and I would say Della Maddalena.
A lot of those guys are kind of in betweeners, where you'd be in safer waters just calling them pressure fighters.
