Doing what Siri is doing is not rocket science. It’s a simple intent based system where you give it patterns to understand intents and you trigger some API based on it.
Once you have the intents parsing, it should be just a matter of throwing man power at it and giving it better intents.
Yes, I have experience with building on top of such a system.
But the group managing Siri has probably been gutted in the past 10 years, and while the core is always simple the integrations and the QA testing to make sure it all keeps working is probably brittle and time consuming, and the core code is likely highly-patched spaghetti at this point.
It would be easy to write Siri again and make it a hundred times better, if you could start all over and only write the core features, and not have to validate against the whole product/feature matrix.
The problem with the rewrite of course would be that you won't be able to deliver that minimal viable product any more and you will have 10 years worth of product requirements and user expectations that you MUST hit for the 1.0 release (which must be a 1.0 and not an 0.1).
I've worked on lots of "simple" and "not rocket science" systems that were 10-years old, and it is always incredibly difficult due to the state of the code, the lack of resources, and the organizational inertia.
Once you have the intents parsing, it should be just a matter of throwing man power at it and giving it better intents.
Yes, I have experience with building on top of such a system.