By the time the PS5 comes out, the Switch will have dropped in price and released a budget option. It will also have a fully mature library and a monopolistic hold on the handheld market.
The PS5 will do extremely well. I would imagine that for 2020-2021 it'll do the same as PS4 is doing in comparison with the Switch. It'll be pretty even through most of the year, but the Switch will put on rocket boosters during the Christmas season.
After that, the Switch will probably slow down as it starts prepping for the launch of a successor in early-2023, though it could well be pushed to 2024. Either way, Switch sales start slowing in 2022, but the system still tops out with 100+ million in sales. The PS5 will chug along as the de facto brand for console games and climb up to 100 million itself, though it will be through a significantly longer generation cycle. As for Xbox, I don't know exactly how well it'll do, but I don't see how it leaps over Sony or Nintendo.
That would be how I would see things shaking out.