my argument actually is this.
since first cohort units are 'elite' and 'unbuildable' units, it's a little absurd if when you go to war, among the 6 cohorts of your legion, you have 5 praetorian or urban cohorts and a single, 'lorrica hamata' equipped, First Early Legionary Cohort. I mean, this is quite absurd that the unit with the best morale, 'best trained', are equipped with lesser equipment than others.
another option is that the chevron experienced or killed/casualties ratio criteria. Say, if a unit reach gold chevron, they automatically get an aquilfer. Or if the unit kill significantly more than they received, they get an eagle (for proving their valor).
if not, then at least give it an icon that shows the unit is 'Elite'. That's why i argue that first cohorts should Praetorian (since in reality this actually an elite although i don't recall their do battle in cohorts).
If we stick with history, then after the Marian reforms, all legions should have aquilfer. Since the game it didn't, CA should adjust a little bit

~On a personal note, i'm complete dejected when i found out that the Great Man is actually insane during his last consulship.