Always a fun conversation. Agreed it is fully legal. Outside of whether it should be done? Why in the hell shouldn't it be done? What's the point of having teammates. Don't like it then don't race track or crits.
On the drop back - yes that was illegal forever but IIRC there was a rule change about 2-3 years ago that was worded in such a way that this is now ambiguous. I am sure someone will cite a rule or correct me. Before then it was 100% against the rules to drop off and pace a teammate in a break. You could drop off and join the break but you couldn't pull/set pace. At that time it was also not legit to allow a rider who was lapped to jump back into the pack as it lapped them. That is also now allowed. They can also go to the front and set pace even if they were lapped. That's where the drop back bit gets confusing...
On the track all of this gets even better. I only half know and am wrong a lot.
The easy way to tell is when an old guy is *****ing about something. Usually means it's not against the rules but he doesn't like it because he thinks he should have won but wasn't able to because after doing all that work someone else was able to beat him.....but only because of the help of others. Sour grapes. Get a team, ride harder, or sit on their move as well.