If the switchglaive had its own Iai strike, there would be no reason to use any other weapon.
Low stance light attack is arguably the best lockdown string in the game. Great hitbox, good stunlock, good damage, and can chain into excellent specials.
Mid stance light attack is the most effective kiting string in the game. It has a wide-sweeping hitbox (forward and to the side) that invariably hits short enemies even on uneven surfaces. Great stun-lock properties, can chain into heavy stance for pressure, and has bizarrely efficient ki usage.
Heavy stance light attack is insane. It's immune to guard reflect, does huge ki damage, excellent stunlock and the optional Square-square-triangle hook pull is timed in such a way barely any humanoid enemies can break out of it.
Heavy stance strong attack has good speed for its ridiculous range, can be charged, and overall functions as a superior version of your standard heavy strong, single-hit punish.
It also has its own version of reaper (rapid-strikes until ki is depleted), and light stance gets to be a discount Yata Mirror.
I'm sure there's more OP switchglaive stuff that I haven't discovered yet, as I'm still quite early in the game. But honestly, right now, it feels even more versatile than vanilla Nioh kusari-gama in the days of YOLO bladespin. Far more fun to use and less braindead, but still!
How are the dual hatchets? I messed with them just a bit in the demos, but they didn't really seem my speed, so I haven't really touched them in the full release, yet.