Well, apparently the only thing you miss out damage-wise while having a tome equipped is the auto-damage. While using abilities it's been tested that tomes have hidden dps that equates more or less the damage to the same levels as when using a 2 handed hammer.
Have to point out that if you use a dps meter and check logs, you will find that auto damage ,while not shown in animations, is a big chunk of damage. At one point my auto attack damage for various melee characters was around 30%.