if balance was symmetrical I would have agreed with your opinion, but otherwise I do not, because every faction have its unique stock units, that totally stand out compared to others. The obvious examples would be, pgrens, obers, comets and KT. So logically when you include those units this reduces amount of units available. E.g. comp consisting of several cons,2 zis,2 engies, single katy and an armada of t34 76 gonna be bigger then UKF analog but with comets.
Handling population the same way at all factions does have nothing to do with symmetrical/asymmetrical balance. I never said lets PGrens cost the same population as Conscripts for example, I said let them all cost according to their own overall power level. So yeah one army may be way bigger as another one of course, as long as the overall power level of all units together is the same in comparison to the smaller army of the other player. I just don't like the argument that FF has to be lowered because UKF is a population heavy faction. It should be lowered because its powerlevel is about population 15. There should be no population heavy faction, units should cost exactly the population they are worth in game value. This leads to a small army if each unit is powerful. Again, an army can rely more on munition, fuel or manpower but population should be an independent tool to balance the lategame.
Judging by patchnotes in recent history Jackson was never 15 pop, it used to be 14 before 17th of May 2018, then they bumped it to 16 (read my comment with a spoiler). So I have no idea where you've got this info from.
So it was 14 and went to 16? Seems I didn't remember correctly.