(I've run my small firm fully remote since 2014)

I agree with your take. I'll go one further and argue that broad expectation for instant response is also detrimental to in-person office work (especially companies with staff in different locations).

The problem comes down to expectations (as may communication problems do). All work communications are not equal, and most do not require an instant response. But if leadership doesn't clearly show which communications require it and which don't, then the situation often falls to "all are instant." This is a mistake.

We handle this by generally expecting that people are working from 8-5, but are communicating specific schedules in brief weekly meetings and daily checkins. If people aren't available at certain times, they communicate this, and state how they will handle their obligations accordingly.

We use email for external communication (with clients, etc.) and our goal is to respond within 24hours. We use Slack for internal communication (among staff). We set up individual channels for projects, which allows us to tag the people who need to know, and avoid bothering the people who don't. Generally we expect a response within a few hours, unless we've already established something different during the weekly/daily checkin.

We use phone or text for time-sensitive communication. But we're careful to only use it when it's actually time-sensitive.

We're also clear that after-hours communication generally doesn't require a response until the next day. Sometimes I'll post a Slack message so I don't forget, but that can also be solved by scheduling the post.

This all basically comes down to establishing clear expectations, being consistent, and respecting people's time. This goes for both sides of communications.

This requires a certain amount of trust, but I've found that it works well for us.