Each Pokémon family should count as 1 slot, and legendaries shouldn't be in the Pokédex except in a special section

You're now aware that there are only 355 non-legendary Pokémon families:
Kanto 72
Johto 45
Hoenn 63
Sinnoh 31
Unova 69
Kalos 31
Alola 44

There are also 66 legendary lines:
Kanto 6
Johto 6
Hoenn 10
Sinnoh 14
Unova 13
Kalos 6
Alola 11

The ratios are:
Kanto 8%
Johto 13%
Hoenn 16%
Sinnoh 45%
Unova 19%
Alola 25%