@Draaka
Here is the thing... do you dislike using the word "broken"? If you are, I don't blame you as it gets
abused so badly that it can be hard to take serious. When I use it, I don't just worry about "Deck A versus Deck B versus Deck C versus..." etc. in terms of game balance. I look at the overall balance within the game, including deck mechanics. Yes it is ultimately true that "the game" breaks a card as much as the card breaks "the game", but one can be reasonable when evaluating which is likely more at fault.
In this case,
Shaymin-EX (ROS) was introduced into the game at a time when its "Setup" ability was clearly going to be problematic. The decks that will rarely get strong draws off of it are the ones that rarely do well competitively. For the top decks a
Shaymin-EX is usually a "second Supporter" for the turn. If
Bianca lacked the normal Supporter clause and expressly stated she didn't count against your Supporter usage for the turn, she'd be a staple! For the fastest decks,
Shaymin-EX can effectively be the third, fourth, fifth and sometimes
even more (though quite rare as it requires a lot of bounce effects and
Shaymin-EX and playing your hand back down).
You bring up some decks that you think it doesn't break. One of them I'd have to disagree with because I reject the notion of all broken things being "equal". Pokémon has two mechanics that
guarantee no matter how powerful some cards are, they can see
absolutely no play. One is the Ace Spec mechanic, which thankfully is gone from Standard play, only sticking around in Expanded until that format eventually has a rotation (eventually it'll happen, but it might be years from now). The other is how Pokémon with the same name count as the same card against the four-per-deck limit. So... if they made one Ace Spec (we'll call it "Heart of the Cards" with the effect that you get to take two Prizes when you play it, it would become a staple that everyone ran. If they released another Ace Spec at the same time (we'll call it "Screw The Rules") that stated you may take one Prize when you play it, thanks to the first card
no one would. At least if they owned said first card. Turn those Ace Specs into
Victini-EX with those same effects but as an Ability, and you get the same situation: two
clearly broken cards but because they compete directly against one another for deck space, one would become a staple while the other would sit in binders.
So... would you think
M Aggron-EX was well balanced if suddenly we got rid of most of the current top decks? It does a massive amount of damage based on a
coin flip; as explained earlier I can't call that "balanced" anymore and this one isn't even tails fails (you still do a solid amount of damage with a manageable drawback on "tails"). I certainly don't call
Professor Juniper or
Professor Sycamore "balanced"; the game would have to be radically different so that discarding your entire hand actually was a worthwhile drawback instead of a potential benefit (some decks) and easily managed (most decks).
My apologies for the length of this post. I was even pressed for time and I went into a lot of detail.
TL;DR: Some of the cards Draaka mentioned as being "fine" I also think are overpowered and I explained why. I also explained how strange though it may seem, you can have overpowered cards that see little-to-no competitive play... because some cards are
more overpowered than others.