"Break his tekkai easily" isn't the impression we get from Sanji almost breaking Blueno's tekkai with a concassé, one of his most destructive kicks at the time thanks to the spinning movement. "Almost" means that not even that kick was strong enough for that.The image shows precisely that Sanji could break Blueno's Tekkai easily.
Blueno has an expression of pain, and Kaku said Sanji almost broke his Tekkai with that second kick.
And later on Sanji was also unable to break Jyabura's tekkai, but he proved to be faster than Califa (enough to be overwhelmingly stronger than her in a 1vs1 if she wasn't a woman) and he still surpassed Jyabura by somehow learning Diable Jambe. All in a day's work. It's a very impressive growth rate taking into account that we don't even see Sanji ever train and that in some arcs he also fights less than his crewmates.