Others have mentioned it, but Youmu is tied with Remilia for best raw damage in the game when both her and Myon are hitting enemies. You can also angle Myon to hit enemies in weird spots, all of which can be reset to forward-firing with the press of the shift key. Youmu's human gauge only going to halfway full makes her a beast at farming time orbs as well, which are needed to see all of Kaguya's final spells (at least if you're bad and fuck them up, moving the clock forward).
Yuyuko is just a straight up better version of Sakuya with how much damage her spread shot deals. In many of the game's stages, you actually have to stop firing to allow fairies to summon their spirits if you want the time orbs because Yuyu will kill them before they're able to do so. Shotgunning with her, while not optimal, is another strategy that can deal extremely high amounts of damage to bosses. I think it's also worth mentioning that Youmu has very fast movement speed while Youmu has very slow movement speed, allowing excellent macro and micro-dodging in a single package.
The only hangup are their bombs, which are still good but not great (they're the only team that's not able to clear a Mokou non-spell with a single bomb). You get an extra bomb after clearing a stage with less than three in stock, though, so that kinda makes up for it. They're also somewhat difficult to use with focuses and unfocused shots being swapped, but absolutely worth it if you put in the time to doing so.