Saying that Kayn/Rhaast W CC "snare" (it's a knockup man) or ult to leech on enemy is like saying any fighter with some form of hard CC is good for support.
Kayn is a fighter who can turn into a carry assassin or beefy fighter, both of which are 'not preferable' as supports (as a support main I know this very well). You say new meta is a thing, then why are you complaining about Lulu jungle?
Kayn is a new champion and thus yes, you can say no definitive lane has yet to be decided, but just by looking at his ability set you can tell he works amazingly as a jungler purely due to his wall-walking ability. He could potentially be a mid laner as his E allows him to roam and he has comfortable damage and as Rhaast you can potentially go top due to him having a beefy fighter nature.
You don't really use Kayn as a support, both forms just don't suit it. The most effective supports are either 'squishier' utility casters or tanky CC monsters. I happen to have one up my sleeve for each; Nami as the utility caster and Thresh as the CC monster.
Kayn has damage supports don't need, Kayn has inferior CC compared to other tanks, Kayn has little to no teamplay utility.
I really don't see why you wanted to play Kayn support. I think you just want to play him as much as possible since he's free, like one of those people who instalock him in lobby and fill; as long as you get to play Kayn the champion, it doesn't matter how inconvenient the role you're playing as is.
That's kinda being selfish dude