You gotta realise, in guilty gear, damage is not your only goal. Bite does low damage, yet puts you in complete control. If you have an opportunity, especially with slayer to take a combo and then say to yourself "this won't do much damage" so you don't got for it, you'll find yourself losing alot.
You should take advantage of every situation that you can. If bite lands you a knock down, that puts you in complete control.
So.. your mixup's failing...well for one regular high low mix up isn't that scary, you need bite/tick thow's and baits to add another dimension to your mixup. It's not all about landing a hit, its also about forcing a mistake. Slayer is extremely good at this, and he has the ability to take full advantage of any hit he lands, whether its huge damage or a knockdown.