I would rather pass a pack of cyclists taking the lane than a tractor-trailor. You can't see past the tractor-trailor to judge when to go to the other side to pass. Much easier with a pack of cyclists. And since they are travelling so slowly, the pass will be faster.
As for a line of cyclists in a single file, one has to remember to do it slowly and then resume speed when you've passed the lead cyclist. I don't think a lot of drivers will do that.