Patreon's perfectly fine as a tool, but only when people realise what it is and don't convince themselves that it's something it isn't.
Patreon is literally just:
a tool to financially support a creator you like. It is
not a platform to purchase a product, it is
not a guarantee of any future content - and that's where I think people tend to slip up, and feel like they've been scammed.
The safest thing if people aren't willing to take a gamble is, like you say, just buy finished (or unfinished but final versions of) content, where you know what you're getting. It's the smart thing to do if you just want to pay for a product and receive that product, and don't want to do the specific thing that Patreon exists for. I will only ever support a Patreon if
a) I've enjoyed some content for free that I thought was really worth X price, and I want to support long enough to pay X price
or
b) I genuinely love what the creator is doing and their design approach etc., and am willing to take that gamble, knowing that just like an investment it may not necessarily be 'successful'
It's rare that I do use Patreon, as there are very few (b) devs out there, and for the (a) ones I can typically just buy the product. But I genuinely think this is the only way people should be treating Patreon, you're just choosing to support them in whatever they do - it's got 'patron' in its name, after all!