Zcash eliminated the need for a trusted setup with the introduction of the NU5 network upgrade. The developer team decided to take this route instead of switching to ZK-STARKS. ZEC is now more decentralized than ever with the upgrade and the removal of the "founder's fee" (which was a sort of tax collected from miners to fund the project). The cryptocurrency is aiming to become a full-fledged PoS blockchain network in the future. This will set it apart from Monero, Grin, and the likes. But I hardly doubt adoption will increase, especially when governments are against privacy coins. They've spread false propaganda/misinformation to prevent as much people as possible from getting into such cryptocurrencies.
I believe both Monero and Zcash have strong privacy methods, but none can replace the other. After all, each method has its own advantages/disadvantages. Which one to use would depend entirely on your privacy needs. As long as the aforementioned coins stay decentralized, nothing should be able to stand in their way. Just my two sats.