Vast majority of the web's downfalls stem from advertising and tracking. Unless you're proposing a way to remove advertising, then the problems will remain no matter what tech the developers opted for.
You are conflating two entirely different issues. Both are true but neither at the expense of the other
They aren't entirely different issues at all and are quite tightly interwoven. It doesn't matter how many ms you shave off by using/not using react when your page loads a full screen video ad and has 50MB of trackers to aid in its quest to access personal info.
One is a tech problem, the other is a business problem.