Ever since Craig Federighi took over Siri as the Senior Vice President that overlooks all software including Siri, Siri has been slowly getting better.
Apple introduced a recent feature to control music without Siri being connected to the internet, but it doesn’t work on my iPhone X and if it did, it would only be to control music and not for other simple tasks.
Siri should not require an internet connection to do queries that don’t need data from the internet. E.g. control music, send SMS, make a phone call etc.
For those questions like “Who is the current prime minister of Australia?” they still need an internet connection because it has to search an online database to get accurate details.
I’m sure your getting the idea from this post and another upcoming post (likely tomorrow’s) that voice to text should not require an internet connection and only certain queries asked by Siri should require an internet connection, but not all!