The Patreon product is 10% payment processing and 90% the marketing/branding/placement/ease-of-use/trust/normalisation, or whatever it is that makes people open their wallets.
If GitHub Sponsors is stronger at whatever-it-is-that-makes-people-donate, that would be their advantage.
OpenCollective for example, being developed via their own platform, need to make sure the platform is sustainable, and can't just throw cash wherever they want to gain marketshare.
The result is a sustainable funding platform that will survive for as long as people fund it.
GitHub on the other hand, can develop the wrong features, spend too much, give cash away and a whole bunch of other things, while not actually achieving sustainability in itself in the long-term. Microsoft will cover all of this, until they wont.
But GH in this space will mean OSS developers will start to get paid for real, the phenomenon will grow and become standard and expected, and if GH stops doing it, the need for it will be so clear and people's expectation of having such a product so strong, that any drop in replacement service will instantly convert most users to their platform.
GH right now is growing the market by bringing millions of eyes onto this problem. The same as Patreon did. And if Patreon dies today, do you think no one will bring up an alternative? And that supporters won't transition with creators to that platform?
It's the same idea as Paypal creating and growing the e-payment system. Down the line, the market of e-payment has grown enough and is legitimized enough that if Paypal was to stop service, there'd be plenty of alternatives, and people are already using plenty of alternatives.
OpenCollective and the likes haven't been growing this market the way GH will be doing, and the result is only a net positive for OSS and developers.
I have never heard of OpenCollective, but I have been using Github for 10 years. And “collective” in the name scares me because it makes me feel like it’s a bunch of street artists squatting in a warehouse in Oakland — perhaps fun and nice people, but not the type of people I’d want to trust with distributing money and compliance.
If GitHub Sponsors is stronger at whatever-it-is-that-makes-people-donate, that would be their advantage.