Would a single browser make the Web fast? No, it wouldn't. If Microsoft Explorer had won and locked down users and websites, would the Web today be fast? No, the Web would not be fast.
Are there fast websites? Yes, I'm typing into one. I think the reason the web is slow is feature creep by both browsers and websites. Diversity is not the problem. Complexity is the problem.
It is very difficult to parse that sentence and come to your conclusion. I'll grant you, the author talks about innovation as well, but not in that sentence. You're free to mark it up to bad reading but perhaps it is bad writing.
Chrome being faster, better and more feature-rich makes users stay in their browsers longer which benefits Google directly (which some might argue is actually a bad thing). But still, Google would have an incentive to not let Chrome stagnant even if they had 100% of the market.