Dear Apple, here is an idea for how to improve Siri. Hire some interns to go on reddit and make a spreadsheet of all of the issues users are running into with siri. Scan r/siri and r/siri fail. Add columns "What was the user trying to do?" "What did the user say?" "Why didn't it work". Now have engineers go in and categorize the reasons of why it didn't work, prioritize, and fix.
You will see many rants complaining about siri. I think one of the reasons it has be frustrating is that it's a two way learning process. Often users find that some feature that once worked no longer works. They stop using it all together and it looses its feature set and therefore value. Or, the user learns a new wording if they can make it work still.
For example, "hey siri talk softer" and "talk quieter" actually have a different outcome now. One lowers the siri speaking voice, one lowers the media volume.
The siri functionality is definitely in flux. They are working on it actively. Things that I know were broken a month or two ago are now fixed and there are improvements. It also breaks at the same time. The problem is once something doesn't work, a human is most likely to never try to use it again.