The dense protag is honestly a genius device for harems: you get to keep the status quo, give the audience someone they can fairly realistically self-insert as, while still feeling that they'd do better and just ask out the girl they liked if they were in his shoes.
My prediction, Nagatoro also fails to defeat Orihara, but instead of waiting until winter to try again, Senpai surprises her with a confession despite neither of them managing to succeed on their tasks.