I was wondering if given the changes to hero skills and moving some of the previous Tome based hero skill buffs to the weapon forging system/dropping others it made sense to tie these unlocks in the weapon forge to the tome rather than the magic materials that you have access to. It does feel a bit weird at times that I can for example give my troops flaming swords but can't do the same for my heroes because I am missing the relevant magic material. This also might help a bit to make tomes have a bit more relevant stuff for heroes.
I could also see it working as an either/or, with the access to either an appropriate tome or material giving you access.