Blueno was a lower tier CP9 member and wasn't even the main boss of that arc. It is not like Luffy went on to insta-kill Rob Lucci right after. Doffy can casually shrug off an attack from Aokiji like it was nothing. I dont really expect their reactions to be comparable.

But I woudn't go as far as to say he isn't the slightest bit concerned. I can see his shock/anger/frustration. But yeah, the element of surprise is probably the main factor in the beating he is currently taking. I am sure he has got plenty left to give, its never that easy against the main villain