@Robby:
If you don't get the mega stone until the post game, and it's locked onto a previous gen's starter, it's not really an "in-game" monster. Same as giveaway legends.
Plus the whole "mega stones take up an item slot and only one per fight" thing.
Similarly, Rotom allows for a whole bunch of different electric types, including a few unique ones, but I'm not sure how much it should legit count for, since you can't exactly stack a team with them, and its difficult to get (generally a unique one per game that can't be bred) and then transform. Just because electric/grass and electric/ice and electric/fire and electric/ghost exist doesn't mean they've really truly been given to anything..
All of the megas I mentioned, which are all of the ones with unique typing, have their mega stone given to the player in-game, so that argument already falls flat. They are all also tied to pokemon that are easily obtained in their respective regions. By your logic, let's not count anything that is difficult to get.
Pseudo dragons happen too late, let's not count them. And have you noticed how you get a beldum from Steven post-game? Let's discard that too.
Same goes for Rotom. To my knowledge the game gives you the ability early on to change its form how you wish, so changing a Rotom form is as easy as evolving an eevee into certain types. But we're not discounting those either.
Legendaries I can get since they're usually restricted in a variety of means, and not something you can count on running consistently in game or competitively. But the ones you are trying to discard from counting just seem like arbitrary rules so that you get to say "I want a REAL electric/grass (or w.e. else)", where real is really only defined by your arbitrary categorization of what has value and what doesn't.