Except a bunch of them have already been introduced and people like them, as I've already explained. Why would they have to wait? It makes perfect sense to me that in the big battle at the end of IW, a bunch of the main heroes are either "killed" or lost in space or what have you. Gone. All the remains, is the new heroes. That would be Doctor Strange, Black Panther, Spider-Man, etc. Then in Avengers 4, they team up, get the old team back together, and finish the fight. We get to see the whole team finally complete with Wasp and Captain Marvel, we get the huge final battle, and we get the passing of the buck to the new team. You can't just go from One team to the next with no transition. You have to have a passing of the baton.
So you think that Chris Evans or Robert Downey has a chance of not being a major part of Avengers 4 until the end.
There's simply no chance of that.