@maxicek *
Cheers!

Funny to read back those posts about crafting. I actually spent
hours gathering data to figure out the formulas. And (with some pride) I can say that the formulas I had come up with actually produced the correct results.

(Although it wasn't quite what the code was actually doing, heh.)
* But yeah, on Whirlwind, I can now confirm after going through the function (rather than just testing) that the "number of attacks" is simply set to however many weapons you have equipped, but other than that, nothing changes. It doesn't swap the weapon or anything. So going dual-wield basically means twice the procs from things like CB, which is a pretty good reason to go that route.
I can't say for sure what does and what does not get included from off-hand, because I know for a fact that there are some bugs going on with dual-wielding. For example I was checking dual-wield skills (Frenzy & Double Swing), and whether you attacked with main- or off-hand, the Eth rune(s) from the main hand were
always applied, whether you attacked with main or with off. The Eth rune from off-hand however was
never applied, even if you attacked with the weapon the rune was in! No clue if there are more stats that are bugged like that. The bug may be with Eth rune specifically for all I know. Anyway, perhaps that there are also stats that you'd expect to get included from off-hand when using Whirlwind, but aren't. Worth checking out, I think!
Edit: I don't think that CB from off-hand is applied while Whirlwinding, though! That's what my notes are saying, at least.

Then again, "Cast on Attack" apparently
is applied. (Or maybe that is meant to say "Cast on Striking".)