I'm an old-school web guy. React is stupid easy, but by nature of things being easy it also encourages really bad habits.
Performance is one thing (the internet is getting slower! Impressively bad!), but also webapps are becoming so incredibly overdesigned, at the expense of the user experience.
Before we had the discrete fields of front-end engineering, design, UX, etc web design was inherently limited and we used standardized shorthands for everything across the industry. With React it's so easy to throw out best practices and try to redesign every single experience from scratch. Combine that with the Figma-fication of web design and teams can get lost making pixel perfect designs that are usability nightmares.
Let's be honest - what percentage of modern React websites actually provide a better user experience than Craigslist? It's fast, I'm not dealing with buttons that move around as a page loads, unusual text sizes at non-standard screen sizes, etc. (The famous McMaster-Carr website is another example).