Earlier quoted context omitted.
Another big gap is the sockets API. Chrome apps have direct access to TCP and UDP sockets. PWAs can't have this for obvious reasons.
What are the obvious reasons? Many game devs would absolutely love to have UDP available on the web in order to do proper networking.
The big issue is trying to make UDP "safe" enough security-wise for the web platform, and such considerations are generally taken extremely seriously. If a vulnerability were discovered, the Google Chrome userbase could become a botnet capable of DDOS pummeling any website.
Workarounds apparently exist for UDP over WebRTC, but it's a very "bulky" solution.