I agree with the OP regarding how he/they handled a rider slowing the flow of a pace line.
Trying to get the group to go around the slow rider is difficult, disrupts the flow and potentially unsafe especially with an unknown riders or riders.
Was it being yelled at or speaking loudly to be heard and responded to...I work in a busy paper mill, we all wear ear plugs and it is very noisy...we all speak in loud voices just to be heard...similar in a way to a pace line as you deal with the riders focus on pulling or keeping pace, the wind in your ears, distance of riders from riders, etc.
It is always difficult when there is a new rider or riders in a pace line of riders that know each other or who have become smooth during the ride.
If the group I was riding with was pushing a pace and working smoothly I'd say something to a rider entering the group and slowing the pace during his/her pull...when they pulled out I'd take a moment to suggest when they reach the point where it is their turn to pull they immediately pull out and cycle back until they felt strong enough to maintain the pace...there is no disgrace from doing that and it is done by many when the need arises...if they were *****y or ignored the suggestion I'd drop them in a heart beat and not think of them again...