Pokemon available to catch by game without any trading: -Emerald: 202-220 -Leaf Green: ~174 -Platinum: ~381 -Heart Gold: ~431 (may include pokewalker) -Black: ~352 -X: ~567 (includes ~100 from friend safari) -Omega Ruby: ~454 -Sun: ~300 -Ultra Sun: ~380 -Let's Go Pikachu: 135 -Sword: ~360
This is cursory research so the numbers are surely off (might include multiple starters and trade evos) but they're in the ballpark enough to make a point.
Doesn't seem neutered to me, there's as many pokemon to catch as there's been in previous generations.
You're looking at it through an extremely simplified lens.
Gen 1 obviously started it all, and thus every pokemon in the franchise was catchable. It already stood out from most RPGs due to the fact that every single monster in the franchise was a potential member.
Gen 2 was designed almost as a direct sequel and compliment to Gen 1, with old pokemon even being transferrable back to Gen 1. So the idea was that you could collect every pokemon with both a Gen 1 and Gen 2 game complimenting eachother.
Gen 3 is similar in that R/S/E is complimented by FR/LG and the GameCube games. Between these games you could collect every pokemon in the franchise.
This pattern continued all the way up until Gen 7. All the games on DS form an ecosystem where you can collect all the pokemon with just the DS games (and Pokemon Ranger, for some reason), and then all the pokemon games on the 3DS form an ecosystem where you can collect all the Pokemon on the 3DS.
And of course, throughout all of this, veteran players are rewarded by being able to transfer their pokemon across the different consoles (with the exception of Gen 2 to Gen 3, for technical reasons), which furthers the feeling the that your pokemon are tangible beings you can keep with you.
The Switch games should be starting their own brand new ecosystem: For instance, they could have made it so you need Let's Go in order to aquire the Gen 1 pokemon that don't normally appear in Galar, just as you needed FR/LG to compliment R/S/E. But that's not what they're doing...most Gen 1 pokemon simply aren't in the data for Sw/Sh at all.