This isn't really a fair comment on DVOA rankings. They aren't opinion, it's a formula.
Rather than being based on traditional metrics, it measures things on a per-play basis. It rates teams based on how successful they are per play compared to average, adjust it by the team they're facing, and then weight it based on how recent it was.
In the case of Dallas and Tampa Bay, both teams are being carried by their defense (and in Dallas's case, special teams) while both have below average offenses.
It's not a perfect system (none are!), and I've gone into issues I have with it before, but I do find it a more interesting metric than traditional power rankings.