Thats where your wrong see. Your wording it far too hasrhly. It's not "NEEDED" .. It's just helpful, very helpful. I mean the things that take a long time to kill are more often then not, things that have high DR.. In which case any old trasnmuter will kick a greensteel weps butt... So it's not that those weapons are "needed" its that there better.
And with the amount of constructs, elementals and undead in the game. I can't recommend a build that picks up a feat solely for the purpose of an xtra 1-10% dps on select monsters, at the cost of some heavy farming time and the stunning blow feat.
Because like I said, unlike khopehs, dwarven axes are easy to get. And no you do not need every greater bane like I have.. You'll do fine with your standard easy to get weapons ,and if you do get 1 or 2 greater banes later, all the better.
I actually just hit lvl14 on this build and already have more then 60 greater bane dwarven axes, including many nice +4 elemental ones and even a couple +5 elemental.. I was really surprised how much more common and less expensive they are versus greataxes.. And vs khopesh and heavy picks? No comparison..
Last check of the auction house:
Dwarven axes - 14 pages filled with excellent greater banes and low prices
Khopehs - 7 pages, few greater banes, all rather high prices
Heavy picks - 3 pages, not much at all.. Reasonable prices tho.
I think the market for khopesh is very demanding on khyber, ALLOT of players seem to be fighter type khopesh users, relatively few axe wielding barbarians in comparison.