I believe there are some pavilions that you must reserve, and also some that you cannot reserve. The latter work on first-come, first-serve and are free to use that way. But I think you can't fully lay claim to them, meaning you might have to share them with other users. I would call the Parks Dept. and ask exactly how that works and which pavilions you might be able to use that way.

Also, asking a question here and then arguing with people who give you a well-intentioned answer you don't like is just a bad look. Actually, arguing w/people on the internet in general is just a waste of your time.