>> Third, it's a file storage. This is the most overlooked part, unfortunately.

When gmail first launched I remember it having such relatively high storage space that my friends and I used it extensively as a music sharing/storage system. An mp3 was just small enough to make it a comfortable email attachment and the storage space was great in an age without infinite cloud hosts.

Huge amounts of gmail's early utility to me was simply the file storage. Lots of people would give you a free email address. Google made a big deal out of the massive space they offered.