These are very great points you brought up! I will try to answer them to the best of my ability :)
Most of the time though, other lanes couldn't care less and here's where the coin flips, the one with the problem becomes the ADC alone, hell, I'm pretty sure any player would love to receive help from time to time!
I think what you mean is the ADC in this specific case is the one mostly affected by the decision. In that case, wouldn't their opinion be the most important? Sure, the other lanes may want help, I mean who wouldn't love extra ganks or extra help to dominate lanes? But is it fair to push aside the ADC's feelings in this situation when they're the ones greatly affected by this decision? Just because 3 of the 4 teammates agree to your strategy doesn't mean it should still be okay. I feel like if the ADC was okay with it, but top wasn't, then maybe that might be okay to go through with since you don't have to bother toplane to still pull off your strategy. But if your strategy directly involves someone else, I think it would be best to make sure they're okay with it first before doing so.
Popular opinion has a weight on reporting but given that a lot of ADCs hates him and that the rest of the team doesn't really care, you end up with a crazy negative score for something that's wrongfully judged
Half right on this. Popular opinion matters somewhat (mostly on behavior issues), but on grey area cases like this they're usually reviewed by a Support Staff. I'm sure more than just the ADC reported him. This strat also affected the other lanes and jungler, so perhaps they asked him not to and when he ignored it they reported him? We don't know. But you don't really get a "negative score" when people consistently report you. Basically, depending on what you're reported on the system will create a file on you for that particular category. If this player shows repeated behavior and receives reports due to it, then the account becomes flagged for review by a Rioter. Hence why he didn't get instantly punished, and why he received a warning. Granted, the Support staff didn't handle it correctly from what I read, but either way it wasn't instantly punished, and since this is such a very rare case the report system doesn't really take that into consideration.
But do rest assured that no matter how many times people report you, unless you aren't actually violating any the of terms and not disrupting the game then you'll be fine. Even if your account is flagged for review (like say you only play Teemo Supp and every ADC reports you), it's still reviewed by the Support Staff and decides whether this is actually a problem or not. If there is no issue, the case is thrown out and nothing happens to your account. I hope that makes sense.
There was a time during season 1 that the figure of a jungler didn't exist, Riot saw that there was a potential role in there from watching people play
This is very true actually! For awhile jungle used to never exist, so I'm glad you did bring that up :) However, Riot more so adapted to the trend forming at the time when they realized the great potential the jungle had to the game dynamic. Similar to the support items and jungle items, which also didn't exist. But Riot saw how well items catered to specific roles do, so they improved on it and expanded it accepting it as part of the meta. But only because it become popular and accepted throughout the community. This is why Riot doesn't define what roles are and where every champion should be played because they really enjoy the community experimenting and testing the limits of the game.
I hope that all made sense :) More than happen to explain anything if it didn't. I'm very happy with the points you brought up though! Definitely worth discussing so I'm glad we are