Let's say you bought a deck with gems, it's kinda ridiculous to even think you can't actually have the same amount of gems (or maybe even more) after 4-5 months when the deck you bought finally gets a nerf (if such thing actually happens).
Yes, you can't just simply expect a deck to be tor tier forever, the new banlist doesn't affect me at all because well, those decks were kinda all and I just have plenty of gems to spend on the upcoming mini box.