In a public group that anyone can join without an invite it’s unclear why you’d even want E2E in the first place, so we’re presumably talking about invite-only

In a public group that anyone can join without an invite it’s unclear why you’d even want E2E in the first place, so we’re presumably talking about invite-only groups. In that case, sending old messages to new members may or may not be a desired behavior, but it doesn’t defeat the purpose of E2E.