Nothing. In fact, it's less native (by most definitions, given it's running in a sandboxed environment). That's the whole point of this thread.

What's more native? Running a Python app that uses PyQT, or running a single purpose web browser in a window that calls a sandboxed+bundled Python server and renders HTML widgets?

In addition, OP was talking about locality. In both of the aforementioned examples, they're equally localized (both executing on the machine they're loaded on).