This is because abilities such as Stone Dragon boosts or strikes are based on smashing their enemy so hard they overcome DR. Effective, but not part of Stun Blade's effect. The Stun Blade pierces straight through DR, avoiding it instead of overcoming it, like Adamantine weapons do, making the two compatible. If the effect could pierce through most of a thick hide, the sword could push through the rest if made of Adamantine, but could not go partway in, and then smash through the rest with pure force. It makes sense to me, anyway, but I may remove it.
I'll get to that in just one moment.
One particularly short moment. This was somewhat intentional. This is why it's called Spellblade. I saw your Parivir, and I am a big fan of FF Tactics; I thought 'Hey, Spellblade's could work really well like this, too,' and felt inspired to make it so. I'm considering making a Fencer Base Class that would be compatible with this.
Wow, I thought Ultra Nifty was reserved for major stuff.
Anyway, I like this Initiator Level idea, and I think I'll change it.
Thank you both for the great feedback.