This has been the situation for quite a while - but the info has only just been added to the Wiki. It's interesting to be able to see it all laid out, isn't it ...
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Classes where the class weapons start lower than 20 hp are most of the Caster and Healer classes - for the lower grade weapons, ie stone and wood mostly.
Another issue of concern, I reckon, is if you do /hero skills [class name] you only get accurate info about the classes you're currently in. Otherwise, apparently, you don't get reliable info.