I might be bringing my own biases but I don't think speed is the primary feature of this. Rather, not being connected to Google's data collection/surveillance capitalism system is the feature.
I would think running stuff other than just a web browser is the use case. The device goes from portable web browser to Linux laptop with every tool a professional developer uses at your finger tips (and a web browser)
I've run vscode, docker and node in crostini (the debian-in-a-VM that you can just enable in settings in normal Chrome OS). Worked great for me.
I'm not at all claiming Chrome OS or crostini are without problems or limitations, but I have been very happily surprised at how well it stood up to some basic web dev work.
I suspect that this distinction will be irrelevant to the next generation, as services like GitHub Code Spaces, which provide a full development environment inside a web browser, become more normal.
For that, one would only need a Chromium OS build without Google API keys. But then, replacing Google account login with something else could take some work.
