Please forgive this rambliing response. I’ve thought about this a lot, but still only have 1/3 of an answer. In the end, there may not be a perfect one.
You have hit the nail on the head. “Open” only gets you so far. The general population doesn’t care if you’re “open” or not, so a winning solutions must be a tangible, structural advantage over their competition.
Add to that, open source is stereotypically less user-friendly than for-profit solutions. There are many reasons, but I think this holds up most of the time.
FOSS Advantages
Small companies often beat their larger competitors because they’re more responsive, more adaptable than the entrenched giants. I believe that “listening to end user feedback” should be a strength, and focus of FOSS software.
Data ownership is still important to some people, as is the lack of tracking and surveillance capitalism. Though, there’s an upper limit on this, so it can’t be the primary benefit.
Speaking of the network effect, I believe the Fediverse itself is a key selling point. There are something like 13 million users there today – not all active, but it’s still a good number starting point. Nobody wants to join an empty party, but if we’re bootstrapping on top of a party with 13 million people there already, then any tools/tech/communities have an added benefit of reaching that otherwise exclusive audience.
A Starting Point..
To expand on your third bullet point, I believe the right goal (for now) is not to replace, but to coexist with the corporate/for-profit communities. This cuts deep into my own beliefs, and the work I’m doing. Very few people will throw out whatever they’ve been using simply because there’s a newer (possibly less refined) alternative out there that says it’s “open.” But they might try it out side-by-side with their existing tools, if they have enough incentives. THAT ITSELF is the win. Once newbies are in the door, then the goal is to grow that relationship, and slowly wean them off of the “passive consumer mentality” that you mentioned.
So, what brings people to a new platform? Not the widgets and gadgets on the website. It’s the content. If there’s good content, people will join. If only to check it out during their daily scroll. That’s what Bandwagon is for: to bring cool, new content to the Fediverse. And hopefully, other kinds of art and culture will follow in the future, too. The content doesn’t have to be exclusive to the Fediverse (for now) – it just has to be a new and possibly more direct way to interact with bands and their music. If that gives some newbies an incentive to make a new Mastodon account, it’s a win.