When reading a recent issue of New Avengers, with Spider-Man whining about the Quinjet Carol Danvers confiscated from Norman Osborn because Stealing Is Wrong, and Clint Barton sternly reminding him of the stakes, it further cemented the status of Peter Parker as a naive, idiotic man-child in the presence of other heroes. This has been shown pretty much every time Peter has appeared in New Avengers, even before Mephisto retroactively put him back in emotional puberty; he can't offer the skills and intellect that the other Avengers have. On his own, Spider-Man's effective if relatively unrefined in his crimefighting, but he's just an amateur by contrast with the pros in the Avengers. So his effectiveness is limited and all he offers is lame witty banter.
This made me also remember the difference between the Beast in the X-Men and the Beast in the Avengers. In the X-Men, Beast is not only one of the originals with more experience than most X-Characters, but the #1 science guy, a talented melee fighter, and a source of moral support. In the Avengers, they have access to many more science guys ( Tony Stark, Hank Pym, Reed Richards by telecommunication, T'Challa, etc. ), so he just cracks lame jokes and buddies up with Wonder Man in the most homo-erotic way possible. Similar effect; he can't compete in skill, so he plays the nice guy/class clown.
And, of course, there are cases like Cannonball's first X-Men tenure and Justice's attempt to join the Avengers, where they're so captivated and starry-eyed to be part of the big leagues that they become self-conscious and screw up constantly. Can anyone think of other cases where a hero who's effective on their own or on a lesser team is portrayed, intentionally or not, as an idiot when in the big leagues?