This ruling limits their options for introducing future mechanics.
BREAK cards and Prism Star cards were released during the last third/final quarter of the EX and GX eras, respectively, and weren't necessarily meant to replace those mechanics so much as introduce some variety. Well, BREAK was presented as a potential counter to EX cards, but I don't think that ever panned out. As others have noted, they have their own drawbacks in how you can get them into play/fit them into a deck, which balanced them in and of themselves.
This means Prism Star-like "one-per-deck" and BREAK-like "counter-meta" mechanics are necessarily going to have built-in power creep if they ever show up again, because they're now by default part of a subclass that many Trainer cards ignore in deck searches, opponent attacks do more damage against, etc.