There's also many email solutions in-between complete self-sovereignty and utter dependence on Big Tech. Exanples include PurelyMail, Namecheap PrivateEmail, Zoho Business, all around $1/month.
This is true, but many of these services use Big Tech in their stack. So it’s a philosophical, security, and personal choice.
Yes agreed it's not ideal just a temporary learning stage before going full sovereign, sort of like transitioning to FOSS while on Windows or Mac before switching to Linux a year later. I guess the trick is not to become complacent in the transitionary stage.