Firstly, I didn't speak in absolutes, so don't add them in yourself to replace my estimates, in order to make the point that what I said shoukd have been an estimate an estimate. To use the term you used to describe those with opposing views, that would be moronic.
Secondly, subs and squad players leave big clubs all the time. Real have had a set front three for years, to the extent they have been given an acronym, and they have had nobody of comparable quality on the bench, let alone anyone who has a very good case for being a better player than at least one. Well, they did have one, and he's currently scoring goals for Chelsea as a result.
Barcelona's front three speaks for itself over the years, nobody joins them to 'compete' at all. Sanchez left when Suarez joined.
Bayern have young players like Coman understudying for players who are 33 and 34. He obviously won't look at the squad and conclude that he can't possibly have a future in the first XI so long as Ribery and Robben are around.
As for City, who knows with them, I'm not convinced their players join them for footballing reasons in the first place, and also, the one time the question really came up, the expectation was that Aguero would leave, given that both he and Jesus can't play together in a team that plays one striker. How has Pep resolved it? He's played them both. Which is what I'm proposing for Rashford and Martial. They very obviously cannot both be first choice left winger. Competition may be fine for a little while, but they won't compete forever, one has to establish themselves, and the other either becomes a sub or leaves. This is a logical projection.