[Ziero]

Dual Weird improves DoT, not the speed of TP gain: It lower the weapon's delay. Since weapon delay is proportional to TP return for each hit, it lowers the delay without changing waepon's base dmg. Thus DW improve DoT while rate of TP gain remains the same.

Note: DW does give an extra hit (offhand) on physical WS. But how often DNC uses WS, depends on play style.

As for DNC/SAM, in theory you can use Hasso in the follow manner:
(1) Have Finishing Moves and Reverse Flourish ready, and
(2) When TP is close to 0%,
(3) Swap in any Elemental Staff, use Hasso,
(4) Swap in Dagger,
(5) Reverse Flourish (or Mediate) to gain back TP.

In the past using WAR/SAM, I confirmed that the effect of Hasso remains even if you swap to 1-handed weapon. You can still see the STR+ bonus from Hasso in the menu, and Hasso Icon at the top of screen.

If that was true then I'm sure SE fixed it by now as that would be one hell of a bug.