I always think of Peter as fairly competent (!) I think because I'm much more familiar with the later books. In Peter's Room - well, he falls off a horse, having maybe jumped too many fences, but deals with his broken collar bone in a stoical manner. (And he's much more sensible about Gondal than Ginty/Patrick). In Thuggery Affair he deals with the Thugs in a fairly impressive manner - eg turfing them all in the river at one point. In Ready Made Family he helps Nicola rescue the younger Dodds from drowning and train crashes.

Not such a bad record!

Maybe he's growing up and becoming more competent as the books progress? Either way I like him tonnes better than Giles, who just reminds me of various arrogant public school types I've encountered over the years...