CDNs are still useful if you (can/do) put everything on the same one. They’re just not useful to serve static dependencies off-site in hopes of users hitting a primed cache from another site, because of cache partitioning. That’s okay, that benefit was fairly limited anyway. You’re better off focusing on reducing page weight and optimizing loading (order, inlining critical resources, tree-shaking/code splitting, preloading to avoid waterfall, etc) anyway.