I agree with your post, good job, except on two points
4. Stupid Theories
5. Supports, and Why They Can Carry (Nope You're Wrong, They Can)
Your whole post seems like a stupid theory, except I don't judge it stupid. You judge others theories like they could judge yours.... I don't like that XD
Also, about supports. 0-1300 elo bracket, supports ARE often reduced not to carry.Why? Because the support gives tools to his team (wards, CC etc.) but he will not dish insane amounts of damage. What his team does with the tools, however, is not in his control, which is why you rely a lot on your team to win. Also, the support is not the only responsible for the ad carry being fed, the ad carry himself has a lot of work to do, and can still carry even if the support does a bad job (it is harder, of course). But a very good support with a very bad ad carry might not be able to win the lane, and if it happens, the support has almost no power on the events. I do often win games with Leona, and sometimes I like supporting, but the reasons above are why I prefer not to.