The DeFi phenomenon is a very cool innovation in the world of cryptocurrency and financial systems in general! However, many scam projects and lack of regulation can ruin this system... That's why they say about a short-term trend and a hype, like ICO 2017...
DeFi appeared much earlier than we imagine. Take for example the same Link that has been working since 2017. In 2017, we considered it an ordinary ICO, by the way, I took part in it then. And only in the Wake of the hype around DeFi, we began to look at those old projects in a new way. So, when the hype around DeFi ends, there will be really high-quality projects on the market that will continue their development.