Consider the following:

>Legends that aren't mascots/mews are considered padding and filler
>Retcon evos and baby pokemon are definitely padding and filler

Gen 1: 148 nonfiller Pokemon
Gen 2: 78 nonfiller Pokemon
Gen 3: 128 nonfiller Pokemon
Gen 4: 69 nonfiller Pokemon
Gen 5: 146 nonfiller Pokemon
Gen 6: Assuming there's still a Mew, 69 nonfiller pokemon, otherwise, 68.

>Odd generations have historically introduced more lines of new pokemon
>Even generations have historically introduced more drastic mechanic changes to the games

Not a pattern per say, but definitely a trend that is very easy to see in hindsight.

>Gen VI's roster additions would be equally, if not more, blasted if it had an additional 30 pokemon that were retcons or legends akin to the Kami trio/Heatran