How does balancing around plat + elo imply that lower elo's input doesn't matter?
I mean, first, ANYONE can suggest improvements to the game (i.e. the interface, new content, etc...). It's Riot's job to determine if the suggestion is worthwhile and if so to balance it, but making the suggestion requires no skill.
Second, new players can use the forums to seek advice.
Third, where are you getting this "balance around plat +" stuff, they balance around the LCS - everyone knows that!
There are also plenty of people who are probably at plat + elo in normals and just don't play ranked or haven't played enough ranked to get there. How many games would it take a plat 2 skilled player to rank up a fresh account from unranked to plat 5? Let's say they go 8-2 in placements for silver 1, they'd need to win 5 more than they lose to get in to each series, and win 2 best of 5s and 4 best of 3s. With a 75% win rate from s1 to g3, 70% from g3 to g1, then 65% from g1 to plat 5, you're looking at about 100 more games after placements, give or take 10 depending on if you win each series first try, to get to plat 5. A skilled player who only plays on weekends, say 3 games per week, would still need nearly the entire season to get to plat 5 even with those extremely high win rates...