"You dont always need a tank. "
I did say I'm not considering what-if scenarios. Yes, you do not need tanks but HP is not a resistance. You're just a damage soaker.
And off roles still exists. Hence Riot bans people if they fail to discuss completely out of context picks without communication with their teammates. You clearly haven't seen major dilemmas where this issue occurrs[Nunu support, Singed smite support, and other Riot threads targeting the issue].
Don't compare mage supports to complete offrole picks. I clearly stated picks that are completely irregular need communication. Those supports you listed and Ziggs ADC are champions the community has abused due to Riot's items and poor decisions that affected botlane. In addition, mage supports are quite common now. These are METAs you are indicating.
"GP, Teemo, Kennen, Rumble, Heimer, Yasuo top and more"
These are considered lane bullies. However, they don't fall off as hard late game due to their utility. Comparing Fiddle with Teemo, Fiddle would not be able to duel an ADC while a Teemo could still shut one down even if they built resistances. Why? Because Teemo's kit can be relocated to other targets.
"Some even bring adcs top"
Vayne top? Lucian top? Those do not have very high winrates. They trade DPS for less utility and more damage. Their early games are actually quite easy to beat one-on-one with most toplaners and lane bullies as well.
You make scenarios seem common but really there's no basis on how common the scenarios you are giving are other than mage supports, MF support which is linked to LCS plays, and poor arguments that reference the meta. I am not talking about the meta.