CAs are still great(against all but Fur Hires), but no one is willing to fork out money to get new ritual boss monsters like Saffira and Vennu(justified because even just to get 3x Senju or 3x Sonic Bird is a pain for your budget already) and many find Fur Hires to be the new budget Tier 0 deck more cost-effective than CA. They're still good at least in theory and experimental match-ups.
Sylvans are technically at the same level with CAs(If you know which cards to substitute for), bringing it to the same levels as Aliens and Geargias, at least in theory and experimentation(which is 1.5 to 2, not bad compared to Fur Hires which dominae at Tier 0). At least it can be argued that it was necessary to keep F2P players in the game. Visit the Duel Links Meta site if you wish to keep up.
So, it comes down to whichever is cost-effective(and new??!!) at the same time that determines the meta. However, in theory and experiments, you only need the core to stay the same while techs can vary, which bring us down to the budget again. Keep in mind that CAs and Sylvans are still in the game, but not as cost-effective as they once were.