Thanks for writing!
Some thoughts — I can’t find convincing evidence that “installability” is particularly useful to users on desktop. Icons are so important on mobile as typing is hard and everything is driven from the home screen. The fact that 87% of time is spent in native apps underline this.
On desktop, that isn’t the case. The web has essentially won and navigating via our current browser mechanisms seems to work well.
On desktops it’s also not clear standalone windows are better for window management than tabs, and when Chrome ran a user study on this we found the vast majority of power users would rather use tabs.
Also note that there are tools for power users to put websites in standalone apps, and there are a few users that really like this but a) I don’t think these are most users and b) the existing tools serve this niche reasonably well.
Concluding, I think the value proposition is murky (but there are some cases where it could make sense) and there’s no existential risk to counter like we have in mobile, so our resources are better invested in improving PWAs on mobile.