I don't consider someone who's simply leveled, or even half-heartedly geared a tank class to be "a tank" in any way what so ever.
To be a tank, you need to actually use it, abuse it, love it, hate it, ride with it. You have the prestige, the responsibility, the leadership, the ability to be the target of everyones hate (and you thought you only needed a mobs enmity!) and walk it off like it's nothing.

In this sense, the shortage of tanks continues to be an issue and is overall real. Unfortunately, it takes a certain kind of person to be a tank (this also applies to healers), and there isn't much you can do to get people to change over to one. Even Dark Knight tanks will go through the same trials of their peers all other tanks end up going through.