The Kled animation seems rather PG compared to the lore Riot has been dishing out over the past year

I doubt it considering he straight up murdered someone with his axe-bayonet and blew someone to literal smithereens. The focus was on showing Kled and Skaarl coming together and setting them up as characters, not to be a massively in depth story in its own right. It's like a couple of paragraphs within a chapter of their stories.

It's probably because of how his character is. This video was made to give you a first impression. It showed you that he was willing to kill and that he loves his mount very much (and vice versa). However, since Riot didn't include tons of blood, I don't think it's in his character to just be some bloodthirsty killer. Insane, cold, and maybe even irritable, but he's probably not some huge killer. If the trailer included tons of blood, you would remember his character along with it and have that image painted in your head with his character. Riot obviously wanted a little bit more of a crazy, cooky, funny, and insane approach to this character rather than bloodthirsty or serious.

Between the cliche music and dull animation (impressive detailing though), the video did not make me interested in him what so ever. Dragon trainer tristana's pet looks more lovable, to be honest, he looked like a midget dwarf.

It's because Kled seems to be a more comical character,thus they made a more comical video.