You are remembering it wrong. What they probably said was "invest into Warfare, not Scoundrel", because Warfare boosts your physical damage and is therefore better to max than Scoundrel.
Since daggers damage scales based on Finesse, using daggers as your weapon while pumping STR strikes me as a Bad Idea.
But you know what, let me just test this with my level 21 characters moving my daggers from rogue to warrior:
On Beast, my Rogue:
STR = 12
FIN = 45
Warfare = 1
Dual-Wielding = 7
Damage = 715-750
On Red Prince, my warrior:
STR = 43
FIN = 14
Warfare = 13
Damage = 508-534.
In conclusion, For FIN-based weapons, you should boost FIN, not STR.