I'm perfectly fine with intuiting that better kda ratios will be correlated with win/loss, and I expect most would be satisfied by that as well. Anyone who plays the game knows that a good kda doesn't assure victory (and indeed theres plenty of cases where the entire team can do poorly, but a 'lucky' ace can be enough to let a team kill the nexus from behind), so it's known it's merely a correlation and not a causal relationship. As such, I don't see what there might be to gain from exploring how strongly correlated kda ratios are to game outcome, but you are of course free to approach it if it interests you.
That said, I would propose that measurements of Kills/deaths/assists individually as you're doing would be a better indicator of game length than game outcome.
We already known that LP awarded versus KDA is unrelated, since Riot already told us what it does depend on (i.e. the things I mentioned in my first post). If you or anyone found that there was a strong correlation, then that would just indicate that there was a confounding factor in the data (or simply there wasn't enough data).
Science/research/etc is cool and all, but you have to be careful if you want it to be meaningful. Confounding variables are in abundance, particularly with such a complex game as league, so you really need to be careful to control for things. On the plus side, there's lots of things we know about league (since riot told us), so that can make things a little easier than the messy complex world that is real life, but it's still somewhat more complicated than slapping some variables together on a graph and looking for lines.