Weapon Ratios

[Synthlol]

Since anyone can remember, the standard for judging weapon quality (in terms of swing damage output) has been the ratio of its damage to its delay. Of course, the main hand damage bonus encourages faster weapons in the Primary slot, but for the offhand weapon, the advice is invariably to "use the best ratio" to maximize dps.

I have to ask: Has it ever been proven that (barring the MH damage bonus) equal ratio weapons produce the same damage output in the long run?

It doesn't seem to be self-evident that damage and delay carry equal weight. How do we know that in the offhand, a 10/20 and a 15/30 weapon average to the same dps? I'm no expert on the formulas that control swing damage.