Professor Oak has always been kind of a jerk. At least that’s how I remember it, but he does have a point. The only real way to catch ’em all is to connect and trade with yourself in an alternative universe. Am I right?
Don’t forget about how many of them don’t even appear in your game at all, and which ones those are depend on whether it’s Red or Blue.
When he says all 150 he’s also talking about 1-149 + Mew, because if he knew Mewtwo existed he’d also know Mew must be real, which means he’d know there was 151 Pokemon. So he’s asking you to capture a Pokemon that isn’t even in the game that most people think is nothing more than a myth.
I always thought it’d be better if they made a point of telling you several times in game and in promotional material that there were only 149 Pokemon (or less), and then Mewtwo would be a surprise addition the player could take the credit for. How awesome would it be if you went into Cerulean Cave because it was rumored to be the only place to get the Amber for an Aerodactyl, but when you go to grab it Mewtwo comes in seeking a battle with the strongest trainer alive?
Then when you capture it tons of NPCs react like you’ve blown their minds. Aside from when you beat Blue Professor Oak never seemed particularly interested in any of your amazing accomplishments. ‘You captured Zapdos, Moltres, Articuno? Meh. They’re only the three legendary birds, it’s not like just encountering one of those Pokemon alone would make you famous. It’s certainly of no interest to the world’s leading expert on Pokemon’.