The Pulverizor - 20 WF Kensai Warhammer Fighter

[Logic]

Logic: you're correct
The power of a barbarian is that you don't need to spec in a weapon... so you could use Warhammers for trash, and Khopeshes for bosses. (you would just take the -4 to-hit, since Barbs don't have any extra feats)

Exactly. If you're gonna switch around weps situationally then a barb makes more sense. Only time I plan on switching weps is to bypass DR/slashing

In the end:
I did the math a bit ago: your Stunning Blow DC will be slightly lower..but not by much

Except, as far as a stunning blow DC comparison between fighters and barbs go

Fighter +8.5 DC, +12.5 DC when power surged
+1.5 (+3 str enhancements)
+4 (stunning blow enhancements)
+3 kensai
+4 (+8 str power surge, situational)

Barb +2 DC, +10.5 DC when raged/frenzied/death frenzied
+1 (2 str capstone)
+5.5 (11 str rage, 8 and 3 enhancements)
+1 (+2 str frenzy)
+2 (+4 str death frenzy)
+1 (+2 str from frenzied berserker ToD ring)

Fighters power surge lasts 1 minute, barbs rage lasts for about 4 minutes.

So I'd say that the barb has a slight DC advantage over a fighter.