That's the thing though, those forecasting doom never claimed that "support will gradually shift away over the following years" or anything of that nature.
It was always essentially "when PS5/Nextbox release, third party support will vanish/drop off a cliff."
Don't know if I've seen that specific line, but I think there's also a chance you may have misunderstood something?
Because you listed some third party exclusives. And I can't imagine people were referring to that, right?
The reasoning behind such comments would be that it can be more difficult to port games designed with PS5/SX in mind, than it is to port games designed with PS4/XBO in mind.
So in other words, current gen multiplatform games.
There's little to no correlation between PS5/SX and the continued interest in releasing third party Switch exclusives, or ports of older games to all systems, etc.
People can also use terms like "When *insert something* releases", while not meaning the literal launch date.
For example, according to several development studios, we're only now in this year going to start seeing the majority of the effects the pandemic had last year.
And a lot of games coming out in the next year or two began development before PS5/SX were announced.