I simply can't get around Proton's pricing model. A lot of services already work with rclone, which has a crypt backend on top that encrypts everything stored in the cloud. With ProtonMail's current Visionary plan, you get 40GB of storage for $30/mo and with ProtonDrive it looks like you'd get maybe 140GB of storage for $30/mo. G Suite is $12/mo and you get unlimited storage. If you're worried about security, you'd simply use GPG on top of IMAP or Mailvelope.