How gullible is the League community?

It's a little difficult to pull this off because there aren't several dozen prospectors annually for the various professional teams or vague changes to champions. All of the information is more accessible than public domain; Riot and the community has seen to that.

That being said, the community more often than not fools themselves by giving in sooner than one sanely would by proclaiming that about half the roster is broken and uncounterable, attempting the same tactics on different champions and expecting similar results (Yasuo can kill squishies in seconds, so he should kill tanks in seconds, too), or overspecializing and paying the price for it when it doesn't work. (all AD melee assassin)