The beauty of a game that involves multiple people is the very fact that it involves multiple people. Many opinions, many views of how the game works, how champions are to be played, how they are to be build, etc. I also feel like it should go without saying that you're merely taking a shot in the dark by saying the developers or otherwise don't play the game, also, why does that matter? The importance lies in the players, not specifically what the developers personally experience. We're literally playing with numbers here, in terms of the champion, the items, and everything in between.
We're the very bits of information they need to reach a conclusion. It's why it's a popular notion that they rely on high-elo/pro gamers to reach a more sound conclusion, because the results are a bit more finite to the intended and unintended use of anything within the game's boundaries. It's why we have PBE, it's why we have such outrages results within the first week or two of something's release or change at least, before any potential changes or otherwise take place. It's necessary.