I don't even know what a "radiant" mount is, let alone an "apex" one.
If you're talking about those nasty looking gummy mounts, thanks, but no thanks.
Goodness, those things are butt ugly.
Gummybear mounts are the current ones but there has been different kinds in the past, dwemer and fire atro being the ones that come to mind. Oh and the whooly ones wearing rags and breathe frost.
I have the psijic horse from a free crate.
Which is incredible luck. Firstly because I never buy crates, so I only get the free ones which makes my chances of getting an apex mount tiny. But more importantly the psijics are the first apex mounts I've actually liked, and even then it's only really the horse, senche and wolf I like (I don't like the animations for bears and camels and the psijic guar doesn't suit any of my characters). So getting one I like is unbelievably lucky.
It's funny, my sorcerer always acts so serious and mature, but he's not above showing off a bit by summoning a magical horse.