Alright, hear me out here. Peter Pettigrew became a Death Eater behind everyone’s back. He was a spy for a whole year and no one suspected him, his friends still trusted him to the point of choosing him as Secret Keeper. The Potters were murdered, but Voldemort fell and he knew Sirius was aware of his betrayal. He took Voldemort’s wand and hid it, then he couldn’t have had much time to come up with a plan, but he did. When confronted by Sirius the next day, Peter managed to kill 12 people with one single spell, while simultaneously framing Sirius for his crime and faking his own death. Everyone bought the story completely, Sirius went to Azkaban and he managed to stay hidden as a rat for 12 years (3 of which he was very close to Harry Potter the whole time). This was the perfect crime. And then, when the truth finally came out… he managed to escape again. Alone, after 12 years living as a rat, he retrieved Voldemort’s wand, fled the country and somehow tracked down Voldemort who was hidden in a forest in Albania and didn’t even have a body. Before even finding him, he ran into a Ministry witch and figured she’d be useful, so he overpowered her and took her over to his master – and this gift from Wormtail is what made possible Voldemort’s entire plot in the Goblet of Fire. Now, Peter managed to restore him to a baby body. Peter had to be the one to make sure they survived and follow every instruction to their plans: taking the Riddle house, retrieving Crouch Jr, capturing Moody and finally completing the ritual to restore Voldemort’s body.
Now consider all that and imagine thinking of Peter as the dumb, useless marauder. He most definitely was not.
