I would expect Siri to be able to do anything on the iPhone that I can - change settings, report stats, kill/launch apps, etc.
It would be nice if it could control 3rd party apps too, like GMail, but being able to control the stuff that Apple themselves have built doesn't seem a lot to ask.
Apple is somewhat privacy focused, allegedly. I would imagine that letting an unpredictable LLM read whatever system data it wants is not something they want to partake in.