Elementz has a really strong, solid opinion on the lists he makes. He's a more skilled than average player who simply gave his feedback and has been around for a while. He's got a good grasp on game design for the most part and has a front row seat to all the characters in the game at their very best. That's how his opinion is formed.
The reason it happens to coincide sometimes (not nearly ALL the time) with Riot's choices is because his observations are well-found and of considerable concern to the community no matter WHO says it. He just happens to be more proactive in calling it often and thoroughly enough for it to bear argument.
That's my opinion anyway. I don't agree with everything he says but I've often agreed with things Riot has taken care of based on the streams and trends I've seen popping in from the high Elo. They rarely take -1200 elo opinions into account because a great proportion of us do NOT push the characters to their full potentials.
When a company that develops airplanes wants to test their products, do you want them to hire some fresh-out-of-training pilot who CAN fly a plane if you let him or would you want a test pilot with thousands upon thousands of hours of experience in a huge variety of vehicles? Who's feedback would you find the most valuable?
This is an extreme example but that's pretty much how I see where Riot's directive comes from.
Elementz just happens to make good predictions based on data most of us do not get to see.