The most frustrating aspect of Siri's quality decline is that super-basic things inexplicably stop working. For years I have been able to say "call <wife's name>" and Siri called my wife. A couple weeks ago she started dialing another contact I haven't talked to in 15 years with a similarly-pronounced name (but different spelling). I had to delete the old contact to stop that behavior from happening.
I mainly use Siri for cooking timers, I really enjoyed the brief period of time where it started flipping 50 minutes and 15 minutes. And then went back, for some reason, but not after I started using things like 14 minutes and 59 seconds or 51 minutes to make it think just a little harder.
I'll sometimes ask Siri to take me to a local address, and it'll instead pick some random address in a city 2500+ miles away and start routing me there like that's obviously what i wanted