That was about the same damage Vegeta's pseudo-final flash did to Recoome. And that attack was way closer to Recoome's power than Massenko was to Initial Nappa, unless you don't have Initial Nappa much higher than 3,000.The reaction to the attacks makes it pretty clear. Nappa might have been scared by the Kikoho but it ultimately did nothing to him aside from cosmetic damage. Vegeta then put a scouter on and was shocked by the 2800 reading, and Nappa actually took the attack seriously and still felt pain from it.
If he felt pain while punching back the attack, imagine if the attack took him by surprise like the Kikoho. It would have done a lot more than mere cosmetic damage.