People who say Mewtwo's easier to catch don't know what they're talking about. His catch rate is exactly the same as in gen 1. The only thing that's changed is we have more tools to help us now.
Legendary Pokemon could dodge balls (yes, dodge, not only break the ball), and the best ball outside Master was Ultra., not Timer/Dusk. Add the fact it's Recover never ran out of PP, Psychic was way too OP, and you had the heck of a challenge.
If you're reading this, CONGRATULATIONS!! You're wasting your time!!