Yea that's what I don't get about the constant clamouring for a DoF. Its practically always based off the assumption that they are guaranteed to do a good job and last long term.
Obviously, among other things, he would be also judged based on the performance of the team and successful implementation of wanted playing style. Naturally, if he does a bad job, he could survive a little longer than a manager, but in the end, he can be easily replaced. I can only assume he would have a big say in who will be a club manager, so he really can't make so many mistakes.
In my view, though, hiring DoF after you already have a manager in place would be an opposite and wrong way to go, so if do go after one who will have a power/responsibilities like in other European clubs it will be most likely once Jose isn't manager anymore.
But, I think it's the right way to go, once we decide. Time of big managers who are taking care of everything is coming to an end. The manager, imo, should be fully concentrated on his team, training, picking a team and tactics. Our way of working is currently not only resulting in two completely different playing styles in a space of just 2 years but is preventing us from going after certain talented managers who are mainly concentrated on coaching and dealing with the first team. In other words, don't have an experience as traditional British managers and present even bigger risk than they would normally have. Especially, as the link to the board is only Ed and he is not a football man.
Btw. DoF would be great for Woodward also as he would allow him to fully concentrate on the commercial side of things.