This is not a meaningful distinction. Users ALSO expect ordinary websites’ data to be sandboxed. Users trust that pornhub.com won’t be allowed to read data entered into irs.gov.
There is also a brand rep issue. If there is a Chrome bug that leaks data, it will be seen as a Google issue. If PWAs have the same problem, it will be seen as an Apple security issue. One that they have no ability to fix.
