Technically, whatever RIOT says is balanced has to be accepted as being currently 100% balanced (since it is their game and all) until RIOT specifically states otherwise. While board goers may have good points, opinions, and observations, unless RIOT validates their argument, nothing they say can be fully accepted as being correct.
As for the idiocy of the board goers. Most of the time they are just posting complaints about how their biggest opposition/counter is ruining their day since they cant beat them more times than not (even if it is unreasonable for their champion to do so). Players tend to only want their role to be OP and for all others to be underneath them. And when they feel that their preferred role is in the shitter, like ADCs in 2017 (well most of them anyways), they spam complaint posts on the boards, even if they are not really correct in their thinking.
Players tend to also mistake easy to play for OP. Just because something is easy to play, does not mean that more complex champions are not just as "OP". You just have to learn them better to get the same level of success. A good example of an easy to play champion is Jhin. Pretty straight forward abilities (aside from the math) and not too timing required (you do not have to spam abilities as fast as possible in order to be successful). His damage and range compensates for his delayed kit (can't increase his attack speed more than the base stat). A good example of a more difficult champion is Rumble. While not a hard champion to understand, he has a heat mechanic which makes him have to pay attention to how often he uses his abilities or risk either being forced to only be able to melee for some time or not gain an additional effect on his abilities.
