This is true. I have heard security people argue that SMTP, POP and IMAP are 'legacy protocols' that must be ditched to better secure email.
It means that "legacy" is meaningless if it can be applied so so many other things.
The fire and forget model is also a big contributor to spam. If email were invented today I imagine it would look more like an E2E system that put the storage burden on senders.
TMTP (my work) is a candidate. More at https://mnmnotmail.org/