I believe EACH skill can be very useful in some way, regarding your playstyle, of course !
So I don't like reading again and again : "this & that skill are USELESS !!"
For example :
I like to have a turn based combat with tactical moves, counting in resistances of enemies (have one character loremaster 5), the surrounding effects, spell effects, etc ... for me that gives me the most fun & satisfaction in D:OS !
For me going for the most highest damage making spells and weapons is a thing I don't care for ! IF I find a better type of weapon I switch the previous one with that new found/bought weapon, but not (always) because of a higher damage value ! If that weapon gives a point in speed, movement, willpower, leadership, strength, intelligence, ... that's also a very good reason for me to choose for such weapon.
So probably battles can be longer because of lower damage making weapons & spells, but some battles can also be fast over thanks to tactical decisions !
Just my point of view