Yeah.. I think the two things I'd look for first on older codebases would be removing and JS shims and looking for larger libraries like moment and similar that

Yeah.. I think the two things I'd look for first on older codebases would be removing and JS shims and looking for larger libraries like moment and similar that can be removed. Expressly lazy loading any graph/chart libraries helps a lot too. I'd probably reach for vite or parcel for a bundler, but using Rollup directly is okay.