Personally, I don't mind how Rtron chooses to have Vestec respond to the relativistic hyper-punch itself. If Might gets spent to shield him, that's fine, and if not, that's fine too. From a narrative perspective, what matters is that Jvan panicked and booted Vestec as far away from Slough as she could do in a moment's notice. We know that Jvan doesn't fuck around too much with sympathy for the pain of others (see Hefin, Basheer, the Rovaick, and even her interactions with Slough herself) and considers Vestec an unpredictable traitor to his own identity. She wouldn't hold back, and she wouldn't want him coming back immediately either, as we well know he's capable of doing for free at any time. So, while he'll survive whether or not he's Might-ing for that shield, the question of whether the Might is appropriate or not depends more on how successful she was in setting him up so that he doesn't come back within a few minutes.

If he doesn't pop back up immediately, then that means that Jvan was successful in her Might use, and suggests that Vestec didn't use his own to counter it at whatever stage. If he does, though, then Jvan was unsuccessful, so that implies a counter (in this case the shield).

Reading Vestec's response:

BOOM!

Vestec exploded on the other side of the planet, evaporating hundreds of gallons of water in an instant. Of course, the waters all around him began to flood in to fill where the water had gone, but the Metatic ocean wouldn't be the same level for many years. Without missing a beat, Vestec drove himself through the planet, tearing a small hole through it and appearing back where he had been. "That was rude."

Vestec didn't feel pain (fair enough) and wasn't slow to return (also fair), but he didn't have to use Might to heal himself or teleport back in. That suggests that the shield successfully blocked at least some of Jvan's effort, so in this case, the Might point is better off spent.