The problem with Mastodon is its protocol is underspecified, therefore interop is really hard, and ultimately the standard, if any emerges, will be decided by big tech companies and will be ridiculously complex.
I think Bluesky has a better chance of being a solid standard you can build on, though I find it fairly incomprehensible, but other people seem to understand it well enough, and I’ve been able to get it to do what I need. Kind of like Amazon’s web service APIs. The designers seem smart, and are accessible (a big plus). On the other hand, I’ve already had apps built on their api break.
Neither one is in a particularly strong position.
Bluesky should factor their API, provide a profile, and a simple API you can adapt to in a weekend, for most common things people want to hook into. And they should commit to not breaking that