But if you take a slightly wider look at supporting creators whose content you enjoy, then not at all. You have Twitch subscriptions, YouTube supports/members/whatever they are calling it these days, PayPal, multiple variations of crowdfunding platforms, etc...
It also seems way easier to start up something like Patreon than a FB competitor.
Here's another competitor to Patreon. They have been crippled by PayPal and Stripe refusing to process payments for them. They sound optimistic about finding replacement payment processors, and it's certainly their duty to their customers to try their best, but so far it hasn't happened. https://www.subscribestar.com/posts/5617
Elsewhere in this thread there are people pointing to indications that Patreon's banning choices were due to pressure from their own payment processors.
It's probably easy to create a Patreon competitor. If you want it to not get shut down, though, I imagine you'll have to implement ban policies at least as strict as Patreon itself. So maybe Patreon isn't a monopoly, but on the other hand, it doesn't make sense to say "It's fine if Patreon chooses whatever policies they like because, if the policies are bad, you can just start up a competitor with better policies".
The relevant monopolies/oligopolies seem to be the payment processors.
I think you're probably right. I feel like it's a semantic argument, but it's still worth having, especially when it comes to creating legislation.
There are other options and it's probably not that difficult for another company to disrupt Patreon's business model. There's still the winner-take-all phenomena in tech that makes more or less difference depending on whether your platform has a broad or narrow userbase. If one were creating anti-monopoly legislation, then this distinction might be critical.
Patreon, like Facebook, has a de facto monopoly. The outstanding question is what is to be done about it.