Not necessarily. Patreon has two payment models - either pay per month, in which case you hope the creator sticks to what they say they'll be doing (and you withdraw your support if they don't and you're not happy about that); or the other option is where you pay when they publish a new piece of content (with a monthly cap). I support a couple on that model. So in that case it is more directly a purchase of some content, even if nothing stops creators from posting it outside of Patreon for anybody to enjoy.
There's also a fair bit of patron-only content from many people - bonus comics, behind the scenes stuff, exclusive videos, requested artwork, whatever.
So yes, you are purchasing arts and entertainment. Just in an unusual model.
If there is no obligation to deliver then there is no purchase. It's patronage, an already well defined concept and the basis for their name. Why must it be made more complicated as "purchasing...in an unusual model"?
There's also a fair bit of patron-only content from many people - bonus comics, behind the scenes stuff, exclusive videos, requested artwork, whatever.
So yes, you are purchasing arts and entertainment. Just in an unusual model.