> have a toggle for normal chat chronology/presentation

It does. https://zulip.com/help/general-chat-channels

But even without that, in a normal threaded channel, you can see all messages in all topics chronologically. IIRC that's the default view when you click a channel in the sidebar.

Here's an example: https://chat.zulip.org/#narrow/channel/138-user-questions the messages are grouped into runs of the same topic, but it's the whole channel.