You're claiming the argument is wrong, then supporting it again.
The person(s) who go over or under the threshold are the ones that make a difference. If thresholds aren't breached by the amount of people changing route, then there is not a very significant difference.
As you indeed state:
"but you can still very much say the climate footprint of each passenger is (total plane print/passengers)"
You can indeed say as much, but "this is oversimplified".
Just to be clear - I am not arguing that we should not pick routes responsibly, with the environment in mind. I am merely trying to ensure we are clearer about what impacts we are actually making and that we are considering all the impacts and not just doing a simple calculation that actually misses out the many complexities of transport.
In transport, we have learnt over the past century to not use aggregate models, as they do not provide the same detail and results as disaggregate models[p.18 Modelling Transport 4th Edition Ortuzar & Willumsen]. We should not lower our standards when discussing emissions and pollution.
This article above is a very worrying case - where the reader is encouraged to shame people for flying, without showing necessary statistics as to whether flying is indeed much worse than other transportation methods.
The person(s) who go over or under the threshold are the ones that make a difference. If thresholds aren't breached by the amount of people changing route, then there is not a very significant difference.
As you indeed state:
"but you can still very much say the climate footprint of each passenger is (total plane print/passengers)"
You can indeed say as much, but "this is oversimplified".
Just to be clear - I am not arguing that we should not pick routes responsibly, with the environment in mind. I am merely trying to ensure we are clearer about what impacts we are actually making and that we are considering all the impacts and not just doing a simple calculation that actually misses out the many complexities of transport.