Sucker Punch is more like a bonus ability than an actual attack. If Seir is attacked once, he'll sucker Punch whoever attacks him. If Seir is attacked more than once, he'll attack one of the people who targeted them in addition to the Sucker Punch. If Sier isn't attacked, or all attacks against him fail, Seir won't attack.
The inertia built up from the spinning and dancing required to use Petal Dance would make it stronger, and the spinning of the parasol would displace the energy ball across the surface of the parasol, making it weak enough to be blocked.
The petals make Lilligant a moving target and also create two barriers: Wind and the petals themselves, both of which would barrage Jesi and slow her down, combing with Lilligant's moving around via the wind created by Petal Dance.