You only get first class tags if you are Diamond MPC members, so I doubt if you get "a lot" of First class tagged baggaged on an individual flight. However, different story goes for Business Class tags, which I've seen quite a few in a flight. Knowing you only need be Silver member, and there are close to 50 J class seats on an average longhaul flight, this might not be unusual.

By the way, do the upgraded pax also get priority taggages?