Keep in mind that this took precedence over the Pokémon X and Y and the Sun and Moon Pokémon, in which you were stuck with their respective Pokédex for a spell, and the rest of them became available later. . All official competitions banned all Pokémon that were not in the Pokédex of their games, and then opened them later. As with Sword and Shield, it was also to test the balance. Once they're done, they made everything available again.
I think the same thing will happen with Pokémon Sword and Shield. They would not make Pokémon Home compatible with all Pokémon species if they did not think they could be imported. The difference is that this announcement was made in advance while they have been silent about it for two generations. If they had not said anything, they would have avoided this problem, even after the release of Sword and Shield.
For the record, I still get my Galar Pokemon game because I think they will all be available several months to a year after Sword and Shield. Anyway, my first generation teams still rely entirely on the Pokémon available in this region. What worries me the most is that Mega Evolutions and Z-Moves may not come back, although Dynamax makes Z-Moves obsolete, except in cases like Necrozma.