Wobbles points out "like other punisher cards, this isn't really a choice. All of an opponent's creatures with toughness 3 or less lose flying."And he's absolutely right. I think this card still has value, but it's not really giving anyone a choice.
(And part of that value depends on this being an instant.)
Considering this is probably only going to be used for combat tricks, what about taking that un-choice and facing it head-on? That is -- the un-choice of "it's always better to stay alive than to keep flying, but die anyway"For each flying creature, its controller chooses one:- That creature loses flying until end of turn.- Destroy that creature at the beginning of the next end step.
Or we could just eliminate the illusory choice:Destroy each attacking creature with flying and toughness 3 or less. All other creatures lose flying until EOT.