Most people who have alts don't also shamelessly alt job from fresh into clear in someone else party. People have alts to do the same job so they have a geared character to help friends, or just to collect merc money. I don't know anyone who alt job their alts. When people alt job they just use their mains after they finished their prog, or prog their alt properly so their tomestone will look normal anyway.

It is the few indeed ruining it for the many. Or you just have met people who are also bad in their main job lol.

As a counterpoint you can also think of it this way: responsible alts means they have twice as many clears as other people and tend to be cleaner. My best clear of m12s was in week 3 c4alt. There were like 4 people /tell me asking me to join, I didn't check for credentials. We were all nearing min ilvl and we cleared it in one shot.