The problem with what you're saying is that most, if not all, other classes don't have to follow such a rigid spec progression to be successful. As to the dps v tank comment; I'm fine with that if Bio didn't go out of their way to assure players that ALL dps specs would be viable. You are agreeing that the vengeance tree is weak with your spec and tank comments. Also, the power tech and Sith assassin are tanks as well and their dps spec is very good. Clearly the Jugg needs adjustments.
The best tanks I've run with have been PT, they just have better tanking abilities.