But that's totally against their "strategic diveristy" policy..
?
I'm pretty sure you're either making up strategic diversity being a policy of theirs, or you're completely misinterpreting what they mean by it.
Riot has never gone out of their way to support more than 1 competitive level build for a champion.
A lot of times they've actually just nerffed an alt build out of a champion when it proved to be equally powerful to their intended build direction. Kat's AD ratios where nerffed when she tried stacking BF swords and going AD, Irelia got a rather famous nerf when she was built as a meta-golem over an assassin, Blue Ez was nerffed when that became a thing, AP Tryndamere was obliterated within a month of the competitive scene catching wind of it, AP Yi was removed entirely from Yi's kit with his rework. Tank Sona and Tank Janna were eviscerated with forcing a ton of AP ratios down the throats of those champions as well, tying their utility itself to AP.
There's obviously some exceptions of champions being allowed multiple build paths at the competitive level (Nidalee's pretty much always had options), but Riot seems to frown on that capability in general, and certainly doesn't make adding it a priority.
Which makes sense on several levels - it's difficult to get a decent team-strategy organized and set to go if you have no idea what direction each champion is going for. It's also a massive feat trying to cram 2 equally balanced champions into 1 champ.
Not to mention actually pulling it off gives the champ a significant strategic edge for the picks/bans phase, as it opens the potential to send them into multiple lanes and fullfill multiple rolls, operating as a major flex-pick.
Finally - a large number of champions only really have 1 build path, so offering 2 is a significant edge in picks/bans, team comp, and itemization over the majority of champs in the game. Vayne is only late-game AD, Nasus simply doesn't have the range or mobility to pull off glass-cannon, Karthus is going to be semi-tanky AP every time.
Also her annimations are kind of.. clunky,
that's intentional.
Look at Cait vs. Jax - as a melee you usually get a lot of speed and finesse in abilities, as ranged you usually have a lot of delay - which gets more extreme either direction you go.
I'm pretty sure QWER speed is actually the main lever Riot's used to balance melee vs. range. And if you look at DotA's champion page - they list the AA animation times and casting animation times, including the point where you can cancel an animation.
Riot's designers are very aware animation times are a huge factor in how champions play at any rate (LoL is based off DotA and many of DotA's creators started LoL).
