I have definitely run into "pull your weight" people in conventions... a lot of them. In one game I had a magic item which enhanced my basic attacks but not my special attacks, so I was using a lot of basic attacks during the scenario. I swear these people were going to have an aneurysm. They were constantly trying to tell me what I was supposed to do next. Chill out and let me play my own character, please! One even had the temerity to say I was holding the team back... but I was running a higher DPR than any of them; and doing it with mostly basic attacks. I honestly don't see how any of these guys have any fun playing the game like it's some kind of SWAT exercise.
They were being stupid in that case because your character was obviously not being a problem, but that attitude is common in organized play for a reason. Far too often, someone using just basic attacks is genuinely holding the party back in an adventure that is written under the assumption that everyone is pretty much Superman. Part of this is the module writers, who in my experience tend to make combat either really easy or really hard, with virtually no middle ground experienced in the few years I played Living Greyhawk, and the nature of organized play itself. Characters that aren't at least partially optimized really do not work at all in organized play, and that's something a lot of people don't get and/or like. It's one of many reasons why now that my schedule has calmed down and I have other options, I tend to avoid organized play. It really is a setting where "roleplaying" has very little room as the DM pretty much has to follow the script and focus on the "rollplaying" aspect because that's the only part that carries over from session to session.