I'm not very interested in arguing over the ins and outs of "user expectations" and Mastodon vs. Bluesky, sorry. I would suggest you try it yourself and come to your own conclusion about whether this is a usable system :^)
For realtime discussions (like this one), I don't think we can call it consistent if it takes multiple minutes for each back-and-forth reply to propagate across instances in the best case (and potentially longer through multiple hops?) because you'll see different things depending on where you're looking and at which point in time.
At least to my observation; I haven't pulled apart the protocol to know why: if you're in a conversation in Mastodon it's real good about keeping you in it. The threading of posts seems to route them properly to the host servers the conversing accounts live on.
I hear your point that slower conversation can be better. That’s a product decision though. Would you intentionally slow down HN so that our comments don’t appear immediately? You could certainly justify it as a product decision but there’s a fine line between saying you should be able to make such decisions in your product, and your technology forcing you to make such decisions due to its inability to provide a distributed-but-global-and-realtime view of the network.
Auto-at-tagging doesn't scale to dozens and dozens of actively-engaged speakers, but neither does human attention, so that's not a problem that needs to be solved.
Seeing the existing convo in real time lets me decide which points to engage with and which have been explored, and to navigate between branches as they evolve in real time (some of which my friends participate in). I do earnestly navigate hundreds of times within an active thread — maybe it’s not your usage pattern but some of us do enjoy a realtime conversation with dozens of people (or at least observing one). There’s also something to the fact that I know others will observe the same consistent conversation state at the time I’m observing it.
You might not consider such an experience important to a product you’re designing, but you’re clearly taking a technological limitation and inventing a product justification to it. If Mastodon didn’t already have this peculiarity, you wouldn’t be discussing it since replies appearing in realtime would just seem normal.
In either case, whether you see it as a problem to be solved or not, it is a meaningful difference in the experiences of Twitter, Bluesky, and Mastodon — with both Twitter and Bluesky delivering it.
It's definitely not as clean as a centralized solution though.