skill
Yeh.
What you're missing is the extra you can squeeze from builds.
For your build, you could run.
Neck - fury
Rings - fury x2
Chest - fury
Legs - fury
Hands - spriggans
Belt - spriggans
Feet - spriggans
2h front bar - spriggans
Sword and board back bar - potantates
Head and shoulder - medium monster set
You could swap bits around and run it as a heavy build of course.
But, what you have there is the damage from spriggans is on the front bar where you need it, fury is on both bars as it'll drop of otherwise, potantates is just on your back bar where you are being most defensive and your monster set.
Even if you ran sets like fury and bone pirate for example, which you need on both bars at all times, the power you get from wearing a monster set outweighs any other bonus another set will give you (even more than potantates, willpower and agility).
Even with arena weapons, you can still run a both bar 5 piece, a monster set, a front or back bar only set (spriggans, lich etc) and then the arena weapon on opposite bar (bloodspawn, bone pirate both bar, spriggans front bar and master bow OR master flame staff, crafty alfiq both bars, buffer of the Swift back bar and mighty chudan).