>having a single rider at the front saves the energy of the teammates
Also (as mentioned briefly in the paper), longer pace lines result in reduced drag for the rider at the front. This can seem counter-intuitive, but it's basic streamlining - the following riders fill in the low-pressure region behind the lead rider, reducing the amount of flow separation. Riding two-abreast is actually slower than riding individually.
A really efficient pace line looks like a team pursuit, with the rider on the front doing very short stints before peeling off and joining the back of the line. This is hugely important for physiological reasons, because it allows the lead rider to briefly exceed their aerobic threshold and then recover.
https://www.sciencedirect.com/science/article/pii/S016761051...