It literally is shown. Prior to the attack luffy was getting completely overpowered in every clash and gesr2/3 couldn’t do shit to Doffy outside of Red Hawk (which law had to give an opening for)
Meanwhile post gamma knife Doffy was getting hurt by base luffys punches.
Luffy get that combo in after the haki clash but then don was kicking his ass afterwards when he was using gear 2 and 3 .
Even after getting that attack from Law don was simple to stronger for G2 and G3 and still beating up luffy .
Which is why luffy went to G4 since G2 and 3 were not working , so if anything it show that attack had no effect on don since he still over powering luffy without G4.
Which is why Oda show even with Don blocking with haki he get punch miles away when luffy went into G4 to show how much of power up it was for luffy .
The first time they meet that was like few moves before luffy get throw off the roof if that what using to say he completely overpowered him in every clash .
Which he was still doing even after taking law damage but G4 was huge factor there not that Don get some huge nerf but showing how much stronger luffy got in G4 before we found out it's weakness.