Attack was aimed at taking out a wounded Whitebeard who couldn't even tag Kizaru. He used a mere finger, one of his weakest lasers, to shoot at him, that's about it. I mean if you want to make the argument it's stronger than his named attacks, then go right ahead bro.
A sword provides an additional mechanism to defend & do offense. If Kizaru was merely defending, he would simply block or parry Rayleigh's attack, yet that's not what he was doing. Kizaru himself was engaged in the offense, with Rayleigh being the one in a defensive stance:
Furthermore, the urgency to get past Rayleigh became even more apparent when he realized Kuma was letting them escape:
We then see Kizaru again thrusting the sword, with Rayleigh parrying/blocking it. So Kizaru again, being the one on the offense.. as it's him who has to get past Rayleigh.
The man himself states it was an actual problem that the strawhats got away. Then we find out he was upset about it to a point he captured 500 pirates to vent out his rage.
So I don't buy the Kizaru simply defending himself, if it was an argument for Rayleigh even that might be hard to buy despite Rayleigh being shown in defensive stances twice. To me it's clear as day that Kizaru was trying to get past Rayleigh, as it was a serious problem that he needed to deal with himself, especially once Kuma came in and started letting them escape.
Expecting him to use the sword, when he's not forced to is just not gonna happen. It's really no different than Zoro only ever using the 3-sword style when his 1 or 2 sword style won't work on somebody.