Right now this is not the case. And while you only need 2 perks in the first row of the utility tree you can make these mercs damn hard offensive.
Think of Quick hands + Bags and belts + blody harvest + fast adaptation + crusher
+ berserk (with this you may score a kill get 4 ap back and then do either a second attack and end your turn with the 2 handed weapong drawn or go back to your shield and do a shieldwall, though in that case you would totally need a way to get rid of your fatique) + full force (you can give that merc heavy armor, as he will only wear the shield when waiting for the next turn)
+ hmm the last perk in the offensive tree is open for discussion I do like the killing frenzy perk but together with another merc with Rally the troops Perfect focus would be better
+ then you still have 2 perks left to spend as you please. If you use the shieldwall thing I mentioned regarding berserk you might like to go for 2 more points in utility with ending on Battle flow which also would work good together with Perfect focus IF you hit the easy critters first.
In which way is such a merc less deadly than any other? I would even say he is more deadly because he has the best weapon for as good as any situation at his hand at any time.
Thing is that the question isn’t whether he’s useful, but whether he’s more useful than builds that don’t go for that combination. You’re not just investing perks, but also stats and the appropriate gear into this flexibility. That becomes a problem when the less flexible guy can do the job better that you have in mind for him. He might be worse at something else, but that’s not what he’s there for.
Like Rally the Troops. Better suited to an archer with high resolve. Only really need to give him a stun weapon + shield for emergency. Billhook isn’t lethal enough and your melee skill isn’t high enough for it to be an interesting option. Greatsword is useless to him. Quivers are useful instead.