I tend to agree.
The QS or Spear wielding PM feat Monk has 3 options for bonus action attack:
- Second (blunt if spear) end of QS or Spear — PM Feat — 1d4 + Ability ?†
- QS/S in one hand, unarmed in the other — Monk MA Feature — 1d4 + Ability †‡
- QS/S in one hand, light weapon in the other — Inherent Two Weapon Fighting of all PCs. — weapon's damage die, no abilty mod.
† The first two do 1d4 damage. They say nothing about whether or not this gets ability bonus, so, the general rule applies, and that should mean the damage gets the attribute bonus.
The third doesn't get damage bonus by its own explicit text.
‡ Actually, on thinking about it, normal damage is 1+Str Mod for unarmed; the listed die "in place of the normal damage of your unarmed strike or monk weapon." So...
There are times to use all three.
- Offhand whip to be able to hit a target at 10'.
- Target resistant to bludgeoning but not slashing/piercing
- second weapon is magical
- Second weapon is poisoned.
- Want the guaranteed more-than-one damage instead of the dX‡