Frameworks like React are often perceived as accelerators, or even as the only sensible way to do web development. There’s this notion that a more “modern” stack (read: JS-heavy, where the JS ends up running on the user’s browser) allows you to be more agile, release more often with fewer bugs, make code more maintainable, and ultimately launch better sites. In short, the claim is that this approach will offer huge improvements to developer experience, and that these DevEx benefits will trickle down to the user.
But over the years, this narrative has proven to be unrealistic, at best. In reality, for any decently sized JS-heavy project, you should expect that what you build will be slower than advertised, it will keep getting slower over time while it sees ongoing work, and it will take more effort to develop and especially to maintain than what you were led to believe, with as many bugs as any other approach.
Where it comes to performance, the important thing to note is that a JS-heavy approach (and particularly one based on React & friends) will most likely not be a good starting point; in fact, it will probably prove to be a performance minefield that you will need to keep revisiting, risking a detonation with every new commit.