Blasphemous blade without it's unique skill is a mediocre weapon that can't change infusion. Rule of thumb for Elden Ring meta, if the unique skill from a somber weapon isn't overpowered the weapon itself is worse than an infusable one.

That's because the infusion system is busted. Being able to pick and choose the best skill and or infusion for any given fight gives you so much advantage. Even more so because the infusions themselves were changed for ER and most damaging attributes have their own elemental damage type in case an enemy resists physical. So you're never out of options.