Wrong. You're totally taking it out of context. As I said above, that +5 bonus has the cost of a feat (two if you aren't a martial class) plus a healing surge and 50gp every time you want to use it.
It also has the hidden cost of not being able to get assistance from the other PCs on the roll.
Ok, that's just silly. The +5 bonus is a benefit. Yes, it has a feat cost - a feat that gave access to various other effects as well. The question at hand was whether there was a difference between the Alter Ego martial practice and just using a skill check to disguise yourself, and the answer is yes.
Cadfan has some very legitimate points about the oddity of the way these skills are presented in the PHB, and I think my differences with him are entirely a matter of intepretation (and the text itself isn't clear enough for either of us to truly be 'right'). But making the claim that this one ability is worthless because of the presence of the Skill Focus feat, which doesn't encompass the myriad other abilities available in martial practices, is completely absurd. Having handwaved away that +5 bonus, and trying to then use that as evidence that this ability is, thus, the only way to adopt a disguise (despite the PHB outright stating otherwise) is a completely bad-faith argument that outright contradicts the core rules themselves.
You can genuinely feel that this isn't enough of a worthwhile bonus for a martial practice to provide, given the costs involve. (Though I tend to think +5 is a pretty big deal.) But to say that because it isn't game-breaking effective, it means we should throw out the rules of the PHB... sorry, I simply cannot agree with that.