Interesting assumption. But very much false.
You don't hit everytime with a pair of rockspliter on an unspec'd barb, or any character for that matter.
Base TWF proc chance, for the offhand weapon:
20%
So if you get 100 hits, you get 120 total.
For THF fully spec'd:
75% glancing blows.
So 100 hits, 175 total.
Glancing blows wouldn't quite match the rockspitter hits perhaps, but the fact you get more then 3 times then would more then make up the differnece. No the mention the maintain dmg of a THF is vastly superior, even if its only x3 crit (due to base dice, power attacks, racial benefits, str, etc, etc)
In the actual game, even a 100% TWF spec char does less auto crit dps with rocksplitters then a properly build THF with a THF weapon. But for the most part - the character with the best gear would win here, more so then the build, there prety close.