Originally Posted by Prime32
Since your weapon's power is supposed to be relative to your character level, granting a weapon that scales with your class level means that your class features become weaker whenever you take a level that's not in this class, including after you've completed the PrC.
...and granting a weapon that scales with character level encourages dipping too much...? Most class features DON'T scale with character level.
In that case it should scale with class level until the capstones which should tweak it to something slightly better than the last level, but based on character level. Maybe?