The optics of the Shanahan hire were different than what we're talking about though. The Leafs were in a bad place and desperately needed some strong leadership. It was clear that the organization needed a lot of change, and that there was a lot wrong within it. An internal hire in that situation was not a good thing. The team needed someone who could come in with a fresh slate and who wasn't stuck with past ties or internal politics. He could come in and observe and do what he needed to do. Now I don't remember the optics of the Yzerman hire but the Lighting had spent three straight years being in the bottom 5 (actually two in a row bottom two, and then the year Yzerman was hired they were 25th in the league). I suspect they were seeing a very similar thing to what the Leafs, and recognized the need for an outside voice who wasn't tied down by politics or the normal way of thinking that had led to three straight bottom of the league finishes.
I understand what you're saying. You want to make sure we don't turn aside good candidates and ignore them because they don't understand the processes and ways the Leafs currently run. And I doubt they will, but honestly the best candidate is likely within the Leafs. When an organization is running well, succession is best done within. This is because the internal person has likely been developed in their role well, and has a strong understanding of the way the team runs. This is a good thing when the organization is running in a healthy way. It's when it isn't healthy that you need that sort of change, or when the person being succeeded has been in their role at the organization for a long time and change at that point is healthy.
With Shanahan being a recent hire himself, and Lou also only being here for what will be three years, that long term change isn't a need. And the organization by all intents and purposes, is a healthy one. It is far better to set up an internal hire and prepare him for that transition slowly without public pressure, than it is to bring a new person in and have him go through that transition and figuring out the team publicly. The best example I can give you hockey wise is when Stan Bowman took over (though it's not a perfect example since Tallon was fired...but I digress)
It's a healthy thing for the organization to promote internally. An external hire would have to way outweigh the potential internal person. In a very, very big way. And I think you can look at the speculation that analysts have had about Hunter and Dubas being desired by other teams, and the whole hullaballoo about Colorado wanting to hire Dubas, and be confident that our two internal front runners are very good candidates to take over for Lou (if that's even the plan...for all we know he could just keep on going).