Sure but your complaint is about chat apps, not Slack specifically. For the people who "love" Slack it is just IRC but easier.

It's about the proliferation of slack being treated as the primary mode of communication at many companies now instead of email.

I'd much prefer default asynchronous communication than default real time communication (or some kind of hellish mixture of the two).

Too many people preferred emails. I get several hundred a day because every tool and most coworkers are just constantly giving you updates.

Emails been turned into a feed for me and not a 2 way communication channel at most places I’ve worked

at least email has filters, can't do that for slack

How is slack any different in that regard?

Hasn’t been around as long for people to break it.

I don’t view it as any more than a temporary reprieve and will jump ship the next time a new, less noisy but equally convenient messaging medium comes around

That’s fair, but even between slack and IRC I much prefer IRC for real time collaboration and any chat app for one on on conversations.

Slack threads are the worst thing to happen to IRC. Pick a modality. Is it a real time conversation or asynchronous threads? And then having one on one and group collaborations in the same place means both are done poorly.

It also means the notifications for both get mixed together. I want to get notified when someone posts to a group in slack, and I also want to get notified when I have a direct message, but not at the same time.

I love threads. They're lightweight channels. In large, busy channels it allows parallel conversations. I see no reason a thread would be strictly asynchronous or real time. That's an organizational expectation. And anyone who expects real-time responses outside of a call needs to come back down to Earth.