I think a lot of commenters here are missing the point and getting distracted by push notifications (who wants a website spamming them with notifications?) and loading screens (hardly a feature). Apple supporting PWA (Progressive Web Apps) is hugely important because it enables a future where web apps can natively support browser, Mac/Windows/Linux desktop, and mobile iPhone/Android/Windows native mobile with a singl…
When I change my preferred text size through accessibility settings, good native apps respond correctly. If I need voice over support, the operating system knows how to read the view hierarchy to me in a logical way.
When drag-and-drop becomes a thing in iOS 11, native apps will implement that feature well. I think it will take some time for web apps to implement it as nicely (if ever).
There are thousands of tiny details that your web app just won't have. Those details are more important than your familiarity with a tech stack or how long it takes you to deploy something.
You say that:
> By fragmenting development effort, the overall product isn't as good on any platform.
But I would say that:
> By building a web app, the overall product isn't as good on any platform.
I have yet to find a "web app" that I delight in using, though I love many web sites and native apps.