I think in a porn scene the man should bring the best out of the woman who, typically, is the star of the scene. "The best" can mean different things to different people but if she is really into him and gets really turned on by the sex, then generally it makes for a good scene (that is as long as the director and editors aren't completely incompetent). I agree that Kieran often scene steals and robo-dicks his way through a set series of moves. His attempts at comedy are always pretty flat (even by porn standards) and he just doesn't do a very good job of connecting with his partners (it always looks like paint-by-numbers "porn" not very much like in-the-moment passion). In interviews he talks about his thoughts on his profession and he conveys a fairly workmanlike attitude that I think shines through in his performances. I think he's an alright guy but kind of a shitty performer.
Compare Kieran with Manuel Ferrera or James Deen. Both of these guys are what you would call very "present" in the scene. They are quite different from each other in terms of energy, physicality and psychology, but they both are good at connecting with their co-stars. James talks a lot to his partners and Manuel takes a very passionate and athletic approach...the important detail is that the ladies dig it. When they are having a good time it makes for a good scene because there is less "acting" (which 99.99% of porn talent can't act) and more just being human.