Please don't read that as "you can't succeed without addons", that's not what I'm saying.
Re: Clearing with alts as an argument for ease (assuming by alt you mean a character you play less, with a lower ilvl). I don't get your point - You don't walk up to a boss to have it /yell "Haha! Your group average ilvl is too low!" and insta-gib you all. Lets be generous and say your alts are sitting around 495-500 ilvl (as indeed, mine is). You're obviously a skilled player, so you're probably able to get more out a lower ilvl toon than average player. You've already cleared the content on your main, so you know the fights, the tricks, the things to watch out for. I'd expect a group full of alts who have cleared content on their mains to be more successful than a group of mains even with 5-10 ilvls difference in gear.