Xoogler here (so I can’t help with any changes or feature requests now unfortunately) but yes, all of Google runs on Gmail. The amount of email I got as a software engineer there was crazy voluminous. I and most Googlers around me made heavy use of filters, labels, and all the text search operators available (see https://support.google.com/mail/answer/7190?hl=en&co=GENIE.P...). I also learned to operate Gmail purely via the keyboard with the built in keyboard shortcuts.

I’d occasionally have the frustration of not finding what I was looking for, but usually if I combined a search with at least one other operator (who it was from, what label it might have received, etc.) I almost always found what I was looking for pretty quickly.

And as for the signature image attachments thing, I think that’s actually an artifact of how the sender compiles the email, not Gmail. The “has:attachment” operator is one I use a lot and is usually quite reliable.

Hope that provides a little insight!