I finally played one so I feel qualified now!

Backfist isn't going to do crap to your unarmed defense cause... well they are two different skills. But backfist has a nice little feature that makes it seem defensive. What DOES do a lot is Master of Atemi Waza edge which boosts your hand skills a little bit.

What backfist does or seems to do is it cancels one of their attacks and replaces it with one of yours. It's similiar to riposte. It CAN happen with a weapon in your main hand and nothing in your off hand, but I noticed it happening bunches more with both hands open. You'll see an echo like...

You step into SOMEPERSON'S slice and deliver a swift backfist.
Your punch DOES SOMETHING to someone.

There also seems to be ways to make this happen more (by doing assassin stuff you'd normally do anyways).

I typically got four attacks with my hands (dual wielding fists an assassin trick) and then two to three backfists a round after I lowered their dex a little. Sometimes all my regular punches got parried or dodged, but the backfists are unblockable. (I had Master of Atemi Waza and Master of Uraken edges)

Axe warriors are going to tool you until you get enough HP to survive a couple of pincers, mace warriors... I dunno I never fought one but I assume cranial is going to slow you down a lot. Whips and Flails are going to pose a problem if they have ANY idea what they are doing. I got tooled by a 27th level fist user from two pummels. But if you are reaching level 35, ping a sword or fist user with a sleep dart and they shouldn't beat you unless they are just really good. Occasionally the warrior is a fire giant with +str gear and it takes kote, kans, poison, nerve strike, and your momma's kitchen sink to make them drop their first weapon.

I honestly never got my hit and dam much passed 30 and 25 and it typically cruises around 25/15-20. My warriors typically ran around with a 30/30 to a 50/50 and ocassionaly higher. Assassins do better with light armor so they can dodge (watch your weight) and I find hitting often with smaller strikes and not getting hit at all to be as effective as trying to do a warrior beatdown. I also geared for HP because I like having 1000+ hp and I think it's pretty. I also value save vs spells and save vs paralysis higher than damage.

But backfist makes using hands pretty viable, so I wouldn't listen to what everyone on here says. If someone is hitting you more than you are hitting them, you need to switch to a weapon however. You ultimately need to explore tinker and figure out on your own but a little help and outside experience can help you digest what you saw.