React is not inherently slow. It all depends on design practices. Any front end framework that has to make front end api calls to an api to get its data is always going to be slower than. A SSR site with a local database, eg PHP/MySQL.

I would recommend using Next.js though. Who uses plain react anymore? Next gives you all the things you need out of the box. No need to install react router etc.

Anyway by using the modern features of react suspense boundaries, lazy loaded components and using edge caching like Redis, you can easily develop a lightening fast site using React.