I’ve had a similar experience overall. The breaking point for me was about 2 weeks after I set up Apple Intelligence I had a vacation planned and important details were on my calendar (flights, hotels, rental car, etc). My wife and I were discussing logistics of the day we were leaving and she wanted to know what time our flight departed so I asked Siri “What time is my flight on Saturday?”

It was literally one of two items on the calendar that day and she couldn’t answer the question. She kept resorting to trying to search the web for “flights for Saturday.” I tried a lot of other things also before disabling the feature but it was just useless for most basic things.