Absolutely true! We support values coming from the command-line, stdin, and files: https://vaultproject.io/docs/commands/read-write.html So you should use what you feel is most secure given the data you're entering.
Good security software gently herds the non-expert to make good choices. Too many options, especially specialty risky options, don't help that goal.
There's probably a way to do what you have launching an editor with stdin, but I'd probably suggest documenting an example, to avoid the risk of leaving the secret around.
Also +1 to removing the insecure history option. Documenting the stdin to use 'cat' or something that's not in the history would probably take care of that one.