Blocking a Hakiless slash isn’t impressive. Pica would have blocked Zoro’s slash which just cut a mountain if Zoro had weaker Haki than Pica.
We don’t know how Teach scarred Shanks. It probably has something to do with the secret about his body, which is implied to be that he shares his body with the souls of his two sisters. One of them may actually be a competent fighter
Hakiless slash is something you invented from your butt due to your Teach butthurt.
If Shawk's slashes are weak he can't cut a mountain, do you even know how much power and skill to cut a mountain without even Haki? That means Shawk's physical strength would be out of charts like Nightmare Luffy being swordsman still didn't cut mountain. Its your baseless butt saying he can't use Haki no proof on that.
Zolo used CoA Haki to cut Golem Pica Stones, if Haki wasn't needed he wouldn't waste his Haki.
Even then Hakiless G2 Luffy overpowered Boa Marigold's Barrier CoA. There is no stupid rule like Haki magically blocks every Hakiless attack only in your mind perhaps.
Hakiless Hody's bite overpowered PostTS Luffy's CoA as well debunks your butt again.
And still you didn't provide its confirmed Shawk can't use Haki when they were suppose to be superior to original Shichibukai. If Shawk can't use Haki how his sword is not getting broken vs Haki user Zolo's swords when Zolo uses special swords+CoA to block him? Explain.
Teach's barehands showed better attack power than Jinbe vs Ace, unless you believe Teach's skills is better than fishman karate the difference was Haki between Jinbe.
Thats why Shanks hyped DFless Teach, you make excuses from your butt. Teach having a special body only increases his defense not offense, he still has superior Haki to overpower Shanks's Haki defense. Teach clearly used his claw and Shanks protected his eye with his sword but Teach's claw overpowered Shanks's sword, Shanks saved his eye but still got scarred. If Shanks didn't block Teach with sword he would be one eyed like Zolo.