Hi again Ramza, I installed the menu plugin as you suggested and it confirmed that the attack formula is not being properly factored into the totals.
I also tried recreating my setup in your demo file and it seems to run into the same problem. Only the base attack stat and weapon strength are being factored in and not the value from the baseparam formula and the offhand duelwielding damage modifiers are not having any effect. The only plugin I added to the demo was baseparamcontrol underneath the coreengine plugin and I was using the same formula of adding the Mat stat into the atk.
As an aside, your menu plugin looks great and has some functionality I was actually looking for earlier in other plugins so thanks for suggesting I try it!