Weapons can override the base/counter attack of the wearer - that'll automatically replace the combatant's base attack and counter attack when it's equipped. Equipment abilities would make them available as a separate ability while the weapon is equipped.
So, when setting up separate base/counter attacks for weapons, that's where you'd use them - e.g. for using different battle events for animating an attack.
However, there are Conditional Ranges available for use range and affect range, which can define other ranges based on status requirements and variable conditions.
E.g. you can set up conditional use ranges based on equipped weapon or equipped item type.