This isn't about President Obama, is it?
Not directly. It's about context. You want to rate Trump in a vacuum and that's not intelligent just as it wouldn't be to rate Hillary solely by her own actions and not in context with other Senators or Secretaries of State.
Haven't you yourself brought up Secretary Powell's occasional use of private email in defense of Secretary Clinton? That's context, although in that case Hillary took it to a different level. Still, it's legitimate to bring up other cabinet officers and Secretaries who used private email.