Given the way current LLMs hallucinate, and given that Apple (presumably) won’t accept this behaviour in Siri, I’m skeptical that existing technology (or existing technology scaled up) can ever create the Siri Apple and its customers want.
Honestly, I bet your question is exactly what every team adjacent to this problem at Apple is doing. Pointing fingers at each other and saying, "This isn't my problem. This is some other team." It's so egregiously broken that obviously no one inside there considers it their problem. I think this must be rampant at Apple currently. There's just no explanation for how their software has gone so completely to shit over the last ten years.
Siri can't understand or pronounce very well.
A few weeks ago Siri via Car Play responded to a text and sent it without me saying a word or radio on, and with the setting where it asks first before sending enabled. It responding "Why?" to a serious text was seriously inconvenient in the moment. I watched it happen in disbelief.
I think there is a distinction between Siri misunderstanding what was said (which you can see/hear), and Siri understanding what you said but hallucinating an answer. In both cases, you strictly have to check the result, but in the first case it's clear that you've been misunderstood.
To my Apple Watch: "Hey Siri, tell me what the time is in the central time zone right now"
"I found this on the web", watch shows a link to time.gov
The only thing I find Siri useful for is: a voice-activated timer, handy in the kitchen when my hands are full and I am juggling multiple timed process. It does that well about 80% of the time.