Firstly, I've never heard anyone say that Marvel has a set production schedule into 2018. If you have evidence to the contrary, please produce it...
Of course they have films in development, but there is never a certainty of them even being greenlit for production at all. These decisions are made as they assess the success of particular characters and franchises as they are released.
So, to assert that we would never see a film produced using the reverted rights to the Fox and Sony Marvel properties until 2020 is absurd. And that's not to even mention the fact that Marvel Studios would most likely be producing more films per year to fill the void left by the other studios, as I already explained.
Secondly, the argument of "we don't need these characters in the MCU anyway" always read to me as an attempt to cope with the idea of Marvel never getting the rights back.
Do you actually think fans would be complaining if Marvel got Spider-Man and X-Men back? Of course not. So, why even bother with the "Well, they're probably better off at the other studios anyway" line of reasoning? Nobody believes that. Not even you.