Does meeting a partial stat requirement for a weapon give less damage if you plan to attack with the stat you meet?

[FakeSympathy]

For example, Dark Moon Greatsword. You need at least 16 STR, 11 DEX, and 38 INT. If I have 40 STR, 11 DEX, and 37 INT, the game is gonna give me a warning if I try to equip it. If I decided to just swing the sword around like a regular greatsword, and very occasional magic blast, would the physical damange of the basic attack be reduced? I imagine the magic damage will be little, but does me not meeting all stat requirement reduces the other damage types?

I always tried to meet the stat requirements so I never had to worry about this, but with the DLC I'm wondering if Staff of the Great Beyond is worth getting, Which requires 25 INT and 25 FTH. My current build has 86 INT and 12 FTH. If I plan to use just the sorceries and not the incantations, is it worth investing upgrading to +10? Not sure if it will do any better than Lusat's staff +10