To be fair, Warb isn’t saying Cruz himself made the post, with it being his account. Warb said Cruz is responsible for (and therefore has control of) posts since it’s his account, and thus needs to be more careful with whom he gives access, which I agree with.
From my understanding, whether politicians give account access to staff is not the issue, but rather the wisdom of giving access to any-staffer-or-their-dog. To suggest that Cruz has no control whatsoever of his own account I think unnecessarily absolves him of any responsibility over it. It’s his account, therefore he is responsible. If he or his staff gave access to his or their staff, apparently doing so was unwise given the outcome.