Doflamingo attacks Law with sharp attack without hardening = Hardened
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with no damage
Law attacks Doflamingo with sharp attack without hardening = Hardened
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just from grabbing his blade.
I can't remember in this manga there being such a clear cut comparison to be made in terms of haki, both defenders were attacked with non hardened attacks, both defenders used hardening to defend, and both faced a sharp object. If this doesn't convince people that Doflamingo's armament haki was at the least not stronger than Law's then I don't know what does.