I understand the concern. I spent the vast majority of my career not at Google while also involved in open source communities, and I can empathize with this. I think one place we have a leg up here is that we do have documented processes for performing this type of work. It's certainly possible that the outcome of a proposal is rejection, but the hope would be the process does that quickly. We're all human and we don't want to waste anyone's time.
One of the cases that people cite for Go rejecting the community outright is the modules work. My perspective is that could've been handled better, but I didn't have a stake in that. But then I look at the error handling proposals, all rejected, including the ones originating from Googlers. And the iteration on generics, which has been reworked several times due to dissatisfaction expressed by community members of all experience levels. I think it's fair to say that even though there are deciders of what happens, they hold themselves to the same standard.
I hope you'll consider at least taking a look as a hobbyist. It's a large system, so both lots of opportunity for contribution and lots to learn. I think many of us are very eager to work with people outside the team, especially as many strive for more social interaction in general, and I know many of us are individually looking forward to welcoming external contributions. Certainly we can never find out if the process works if no one tries.
edit: redundancies