Sure, thanks for the explanation! I didn't mean to imply that this was intentionally misleading, just wanted to point out that a lot (most?) of people, including mainstream media, are using the term "government agency" with a meaning closer to your first definition. And with that in mind it's valid to say that the exec branch actually does have the power to create / disband agencies.
And even if we stick to the latter definition of the "agency" - it feels like there's a certain asymmetry here. Perhaps EOs can't be used to create a new agency, because that requires new funding to be approved by another branch. But what about disbanding an existing agency? That doesn't require approving new funding, right? So what stopping an EO to disband an agency?