Black Blade of Disaster?

One Spell I've always thought was underrated was the Black Blade of Disaster although for good reason as it's usually only good for some type of Fighter/Mage and there are several other level 9 spells that are probably better.

I lnow that if you have any pips in Longswords it doesn't give you grandmastery and instead on the first attack/hit it will revert to whatever amount of pips you put into Longswords.

Although that's only without mods and it's unfortunate for people on console that Beamdog/Bioware never patched this bug.

My question is if I have Grandmastery in Longswords as a Berserker for example while having two pips into Shortswords & Two Weapon Style will the Black Blade of Disaster work as intended since I would still have Grandmastery in Longswords?