It did fill a gap for a while unmet by a lot of services that we take for granted now. A Mac Mini with macOS Server to host email, calendar sharing, file sharing, and Time Machine backups went a long way towards meeting a small office's IT needs. It's mostly supplanted by things like Google Workspace, Office 365, Dropbox, and proper MDM solutions these days, but wasn't a bad choice up through maybe 2014 depending on the situation.
My memory of the hosted Outlook/Exchange landscape of that time is much more negative. It was expensive, had inconsistent or costly support for ActiveSync devices, had no integration or federation with existing on-premise Active Directory solutions, management consoles of shared/hosted Exchange providers were difficult to administer. Broadband was much more limited, so remotely-hosted mailboxes were a hassle.
By 2009 at least, iPhones supported hosted ActiveSync. I was writing field service software (“sending people places to do things”) for ruggedized Windows Mobile devices. I do seem to remember some of our customers using ActiveSync from hosted Outlook for emails alongside our software.
