Yeah, I think it's the fact that it's so frail, and it's attacking powers aren't as strong as, say, Salamence. What it does have, however, is great typing that lets it set up on common threats of the metagame, as well as vicious priority that wrecks teams with ease. It's by no means perfect, it has it's flaws that keep it from dominating, but it's a legitimate threat that should always be considered.
By the way, that team you've been using is actually pretty cool. Have you considered making an RMT for it?