Bege is very intelligent. His plan to beat Big Mom was great, but it was Big Mom so of course it didn't work out. Respect Bege.
His plan was an on—the—spot catastrophe that relied on elements that fell into his lap in the final 24 hours of the executing his assassination scheme. Caesar Clown's round up was convenient, and in no way part of his original plan. Luffy's arrival was convenient, and in no way apart of his original plan. Jinbe's betrayal was convenient, and no way apart of his original plan. Alladin and his wife getting rid of the tracking—jelly fish was convenient, and no way apart of his original plan.
He basically just had an idea to attack Mother Caramel's picture and that was it. I think he might be really dumb for considering that to be enough to kill a Yonko in front of her entire crew and get away.