Assuming that the Premium Champion Set isn't a thing, Greninja BREAK will be losing 2 important tools. First, it's losing Base Set Greninja, which used the smaller Shurikens with the benefit of not having to be in the active slot. Greninja BREAK relied heavily on this card in order to hit the magic number of 170 to OHKO your standard fare EXs like Yveltal-EX or Giratina-EX. Without him around, Greninja decks now need to waste time searching the deck for 2 Greninja BREAK to retain that OHKO potential.
Another major loss will be Muscle Band's absence. Without it, Greninja isn't able to deal with the bulkier EXs such as Zygarde-EX or any EX with Fighting Fury Belt equipped as easily. Even with double Giant Water Shurikens, you're not going to reliably OHKO EXs with Fighting Fury Belt or the routine Mega Evolutions, and if XY Base Greninja is gone as well, the feat becomes nearly impossible.
While Greninja BREAK can still do what it does, it's going to be losing a lot of things that made it consistent. It won't be a safe pick unless it at least gets XY Base Greninja back.