You completely missed the point. Look at every line of reasoning you gave as to why there shouldn't be a 4th evolution. Each of those is completely obliterated by the introduction of megas.
1) Megas broke the standards
2) Megas are WAY more overpowered than what I suggested.
3) Megas are like digimon
4) Megas made pokemon enhanced in their appearance
5) Megas not only made legenadaries seem weaker in comparison (Mega Kanghaskhan wrecks so many), they even gave some legendaries megas.
6) Megas prove that high levels and experience are not the only way you can evolve (even if this is different to normal evolution)
You was wrong. Gamefreak can do what they like and break their own standards, and this proves it. It also shows that anything is possible, and also highlights how reasonable my suggestion was. Making beedrill and other terrible/mediocre pokemon usable is much more balanced than powering up garchomp, mewtwo, gengar and other ridiculously powerful Pokemon.