He instantly used "Parasite" after saying the attack was powerful, these clashes happened more than once when he fought Luffy and Luffy looked much worse than Sanji, but Luffy wasn't mid air, and he got Law's help and warnings the whole arc cuz he is impulsive, it's completely different. Doflamingo didn't cared about any "Gatling" Luffy used, and he did cared during Sanji's attack in a situation where Sanji was in complete disadvantage, had no knowledge, mid air and near to clouds, as said by Law himself in the same chapter.
Your problems are learning to read decently.
Oda also has the costume of drawing haki when both fighters are using haki, "Hawk Gatling" has haki appearing, so makes total sense for Doflamingo to show it while defending himself.