I think that having a balance of harm and offense will give you the greatest damage output possible.
Harm pretty much increases your damage cap.
Offense pretty much increases your damage.
Harm will give you more of a power increase.
Offense will give you a more of a damage increase.
Both of them work together though!
If you have really good stats from gear, rings, cultivation, cards, and etc. Then it's acceptable to go full harm if you wish.
On the other hand, having a lot of agility also increases your damage by allowing you to do more % damage!
There's several ways to get stronger and do more damage. Everyone likes to do it a different way. My advice would just to be try out different things and see what works for you.~
Personally I like using agility based weapon with offense as second stat (like medkit or spear, etc) and increase stats with cards, rings, and cultivation. Then go mostly harm (throw in a few other pearls like offense).