Do I need the other version's exclusives to complete the Pokédex?
Solution 1:
No, you need a complete Pokédex in order to complete the Pokédex. This includes Pokémon you cannot obtain on your own, such as the starters you didn't pick and any Pokémon exclusive to the version you're not playing. You're going to have to trade for them if you want to complete the Pokédex.