I believe teh writers said the real reason is power, but that it would be covered in movie universe by them both being involved in the Thor: Ragnorak storyline.
I don't really understand what point you are trying to make continuing on, they covered their base in movie universe.
Yeah, what is your point about production dates? Ant-Man was written and filmed and re filmed before tehy got the license back. Jessica Jenes was written and budgeted before the rights got back and Spider-Man was formally introduced into the world in Civil War. So it seems you are a little confused in what you are talking about.
How can Marvel plan out getting the rights from Sony? That literally makes no sense.
Where is the proof, its in the advertisement for the JL movie and the respective movies being made for the DC Film universe. They are making a Flash movie, Wonder Woman movie, and Aquaman movie, we have screenshots of Cyborg as well, and Batman and Superman are already introduced. On top of that all the major ad shots for JL movie have the mentioned characters in them heavily.
Marvel works for Disney, they do what disney says or the ceo gets laid off. Same relationship that DC Films has with WB and you know that.