If we take the qualifier "late game wars", then it's more or less true. Player will be operating at or near 100 prestige, have plenty of army tradition, and likely 100 professionalism (via general spam) regardless. There will not be many nations even willing to engage a few armies of that stuff near each other.Well sure but by that line of reasoning, nothing matters except siege ability and manpower
Earlier combat prowess is more interesting, but so is money.
The relative power added by 7% quantity increase vs 0.8% discipline is very much finiteNone of those factors is anything more than an insignificant rounding error to the final conclusion: 7% more infantry will be infinitely more powerful than roughly 0.8% more discipline. Which lasts for 1 battle that you can fight every few years.