"Talent Diversity" is just a euphemism/buzzword for nerfing and appeasing to the masses. Take Nazeebo for example, a hero was the staple of the pro scene in the summer of last year. Blizzard wanted to "diversify his talent choices" and rendered the hero totally useless. He had one good build, the spider build, and now he's got no good builds because he's garbage. It is for this reason that I think Kael'thas doesn't really need any nerfs either--the treatment that Rehgar is currently getting in the PTR is what every mediocre and undesirable hero in this game should aspire to have. People wouldn't have a problem with Kael'thas if the game simply had more impactful heroes like him. Nerfing Kael is just putting the cart before the horse. When you're met against a strong hero in Hero League, your response shouldn't be complaining that he needs a nerf, your response should be picking an equally powerful hero and punching him in the face with it. If only more heroes actually existed...

I will say though, in regards to Living Bomb/Chain Bomb... perhaps the fairer option would have been to make the ability a targetable area on the ground, similar to Lunara's Q (some safeguard should exist to make sure you're not hitting multiple people before Chain Bomb even explodes though). This just makes the ability more difficult to land on your opponent. This is a treatment that Li-Ming appears to be getting; she has a ton of damage but you need to land her Q, which isn't as simple as clicking a character with Kael's W. Tyrande also suffers from this problem--Hunter's Mark should have never been a targetable, unmissable, non-skillshot ability to begin with.