I've been working across time zones via IM and email since ... ICQ.
I'm probably biased by that but I consider email the place for questions lists and long statuses with request for comments, and for info that I want retained somewhere. While IM is a transient medium where you throw a quickie question or statement or whine every couple hours - and check what everyone else is whining about.
But clearly, thats cultural.
If you keep your eyes on the linux kernel mailing you’ll see a lot of (on topic) short and informal messages flying in all directions.
If you keep your eyes on the emails from big tech CEOs that sometimes appear in court documents; you’ll see that the way they use email is the same way that I’d use slack or an instant messenger.
Thats likely because its the tool they have available- we have IM tools that connect us to people we need (inside the company)- making email the only place for long form content, which means its only perceived as being for long form content.
But when people have to use something federated more often, it does seem like email is actually used this way.