I'm often asking myself the question "If everyone played at the level of this person - would the dungeon be cleared (in time)?" or "If this was a solo-game - would that person beat this boss?" - and if the answer is "No", then I personally find that person and their performance unacceptable and will try to communicate/give advice first, but if that doesnt work, remove the person from the party. Because at that point it doesnt matter to me anymore that the two of us can dou the dungeon.
For me its not about those 5 or 10 minutes either, its about a certain amount of respect and courtesy for your fellow players - and thats whats bugging me the most about those "bad players", that they show a general lack of both self-awareness and respect for the other people in their party.
...I guess you're right with your last part though and I'm guilty of that myself. I cant count of the times I said "Half of those people didnt deserve this clear of A9NM..." - but I also have an intrest to get the stuff done myself, so I wont wipe the group everytime the bard isnt using songs or dots, just to get them out...
Not a fan of carrying people, but at a certain point, I just give up - just how I've almost given up with giving advice, because most of the time its met with such a bad attitude... (and even worse - we have people who are even defending that and are of the opinion that you shouldnt give polite and friendly advice until the person who desperatly needs it, begs you for it!)
So, somedays I might be building the brick wall those people are hitting by kicking them (not that I actually believe that they sit down and think "mmh, maybe I look into my job now after all..."), but somtimes I just cant be bothered and hope that someone else will do that - or that that bard wont bother to many people on their quest of being the worst WoL Eorzea has ever seen...