I’m afraid turbulence is going the way of efficiency wherein a word with a precise definition is used in a variety of imprecise and incorrect ways until it looses all meaning. I’d say that for the vast majority of discussions here, neither word is necessary and should be avoided.

So to compare drag alone vs in a pact, I think the way to describe it is in both cases drag is determined by the apparent air velocity at the bike. Riding alone, this will be the rider’s velocity plus the free stream wind. In the pack, drag will still be a function of the local apparent velocity, but rather than seeing the free stream wind, the rider will see air affected by the wakes of the riders around her which will be lower in speed and more variable than the free stream.* This effect is large as we know for riders riding in a straight line, the second rider sees a drop in drag of about 25% and the fourth one of ~40%.

*I don’t think “turbulence” is needed for the explanation.