Alex Moul but I always say that in these types of threads.
Alex Moul is an amazing shout, he was still rad when he came back from doing music but you could tell he missed out the years were everyone got more stylish and got a bit more fussy with trick selection. I think he'd definitely have been on level with Rowley and Penny, could skate massive rails and do proper mental tech stuff.
Keeping it UK, it's a shame Danny Wainwright never had a part that showed what he could really do, his 411 profiles is probably the closest and even then it didn't come close to showing what he was capable of. Everyone in the US just knows him as the ollie guy but he was also a legit vert skater, could do all the tech/manual stuff and literally never fell off when I saw him skate UK comps. Seeing him skate Lloyds in Bristol when the Osiris team were there was almost embarrassing how much better he was, I know it's his local TF but still.
Last one for now is John Rattray. felt like when he went to America everyone in the industry knew how good he was but he never really got the shine with the public. Another one who could skate vert to a 540 level, good at tech/ledge stuff, amazing style and also skated rails and gaps well enough to be pro for Zero. His Waiting for the World part is pretty amazing but I feel like he got even better after that but his Zero parts never showed it, his 411 rookies is really good too but not a magnum opus.