USDT can bail at any moment and elave you with nothing. When people follow the money and ignore the facts the suffer the consequences.
Considering that most people "follow the money", they might invest more thoroughly in USDT than ETH itself. They don't care if it's centralized, as long as they're able to profit from it. I believe that the stablecoin craze will last for quite some time, until the demise of COVID-19. After that, USDT's position on the market might return to "pre-pandemic" levels. The fact that market cap tells nothing other than the value of all coins in circulation, should not leave us worrying about USDT replacing ETH anytime soon.
All in all, the rise of USDT's popularity in the mainstream world should be more beneficial than harmful for ETH in the long run. After all, Tether (USDT) runs on the ETH blockchain. For people to be able to send/receive USDT transaction on-chain, they're required to spend some "ETH" which serves as a fee for the smart contract to perform its operations. In case USDT goes down the drain, another centralized stablecoin will take its place on the market. Since most centralized stablecoins live on the ETH blockchain, the world's second-largest cryptocurrency by market cap has nothing to lose. Just my opinion