No one is forcing you to play meta decks. You can still play your own decks and even climb ranked. Besides, you cannot drop ranks, so there's basically no loss of progress. Also, if you do not care for ranks, you can just ignore them altogether.
Once again, you will see a greater variety of decks in the lower ranks than you'll ever will in casual. Lower rank is the actual true casual. Casual is not casual at all and, yes, that's confusing, as I have
explained. Besides, even before the lock out, casual had a lot of netdecks and, after the lock out, it has become even worse.
Ranked feels like it's competitive, while casual is just chilling around. Reality is different. Hence, there is no need to grind ranked to unlock casual. You can just stay in ranked and enjoy the game.