Lemme guess
Forest Shadow is Grass/Psychic, or Grass/Dark
Roaring Heat is Fire/Fighting, or Fire/Metal (Metal has to go somewhere)
Bright Tide is Water/Lightning, or Water/Fairy
I could say that the fourth set in 2013 is the last black and white series set in terms of booster packs, but the first XY series set in terms of theme decks, if you know what I mean. It is obvious that the Kalos Starter Set is connected to Black and White Legendary Treasures somehow. Why else would Black and White Legendary Treasures theme decks not exist? Not only that, the Kalos starter set decks are listed in the store in PTCGO, where you can purchase them for coins, compared to the Trainer Kits and the Battle Arena Decks. From last I saw in the packaging, you can't redeem the Articuno EX, Zapdos EX, and Moltres EX decks that are coming out next month.
In terms of booster packs, XY is the first XY series set.
In terms of theme decks, XY kalos starter st is the first XY series set.
This means that for every time a new generation starts, starting with generation 4, it is always 3 theme decks based on the 3 starters, with the holo face card being the stage 2 evolution of those starters. Remember that in the regular version of the kalos starter set, only the stage 2 evolution is a holo.
XY theme decks could have had the 3 starters as the theme deck front face cards, but you know, the kalos starter set exists, so it would be pretty much redundant. Also note that in some set after, whether it be 2, 3, or 4 sets after, there is always some form of theme deck featuring the video game cover legendary pokemon.