Making of the Meta

I started playing a little over two years ago. I played for about six months, stopped, then just picked up the game again about two months ago. My understanding of what "The Meta" is, is the way that players have decided to default for playing the game. My understanding is, based on patches and so forth, The Meta has a settling period after pre-season goes into season. It seems to me, when I started playing the game, and now, that The Meta is that, generally:

• Toplane: Tank or Splitpusher
• Midlane: APC
• Botlane: ADC / Support
• Jungle: Variety of champs that are suited for it. Usually has an assassination combo, or engage for followup, that allow them to have successful ganks. Both, while still being able to camp clear.

A Meta comes about, because going off-Meta will be punished somehow if the other team knows how. So, what are those punishments? I'm seeing an awful lot of ADC mids, and some APC botlane. I'm not experienced enough to know if the Meta is changing for a reason, or if people are going unpunished.

Sometimes it's clear: "let's not have a jg, let's have two go mid" means that the other jungler has free reign on Herald, dragon, buffs, farm, scuttle, just like a bot game. The rest aren't so clear to me, why they fall out the way they do. APC and ADC are generally both glass cannons, so why did the ADC get a Support? I believe I heard because Mages have CC ADC's don't, which adds to their survivability. If it's symmetrical, why aren't top and bot reversed? I believe I heard because Dragon versus Herald.

If I understand why things are the way they are, then maybe I can take advantage. For instance, maybe I'm seeing more ADC's mid, because now you can get two Heralds before the Baron spawns, and we should be looking for that objective when we have an ADC mid? Or, conversely, punishing the squishy with no CC who went mid on the opposing team.

Is there document or video that breaks down The Meta ... how to take advantage and how to punish?