Re: Downey's last?
I agree Timstuff and I think Marvel knows this. That's why they wanted the whole MCU in the first place. They can get more of their properties on screen and hopefully enough of them are successful enough to be franchises in their own right that they can stagger them in such a way as to give certain franchises that room to breathe whilst others fill the void. And they have enough viable characters to do this.
There's no such thing as a movie that's too big to fail.