Since Doflamingo was stronger, yes.
And that doesn't make the damage Luffy did any less impressive.
Did not defend using hardening, though he used it against a Haki-less attack from Luffy.
There is really no way to get around Sanji being treated like a mid-tier character since the beginning of the TS.
How does it not make it any less impressive ? It's not less impressive if you are damaged when punched in the gut compared to actually trying to block the attack and still getting damaged ? That's what a defense is for, it makes all the difference in the world.
Luffy was using G2 and Hardening and got a clean hit on a haki-less/defenseless Doflamingo.
That was not a Haki- less attack from Luffy, Oda doesn't point out the use of invisible Haki from known Haki users. When attacking or actively defending, if one is a CoA user then he uses the invisible CoA, it should be common sense by now. If an exception happens Oda will point it out, like he did with Zoro refraining from using his CoA in order to not kill Monet. So Doflamingo defended himself from a G2 invisible Haki punch with hardening, but unlike Sanji in this case he was not shown to feel the strength of Luffy's attack through his defense, which makes Luffy look only slightly more impressive than Sanji did.
Sanji is treated similarly to how Luffy is treated when he's not meant to fight a decisive batte against an opponent. He's made to use low tier moves ( the spectre was hinted to be comparable to Luffy's G2 non hardened gatling in terms of significance in their respective arsenals and he used fodder clearing moves against Vergo ) to hype opponents that he's not meant to defeat, partially due to plot. Like Luffy not even using hardening against Doflamingo initially or him trying to punch Doflamingo with a basic gomu gomu pistol. Sanji needs to have his full post ts fight, against an opponent that we can properly judge, before we can tell how strong he actually is.
Edited by Sanji, 16 September 2014 - 04:16 PM.