@OutisI was just using spearman as an example, but yes it would be for each melee unit...
And what I would do for techs, with the help of you and @Thalatta over time is, I would have one armor one for spearman, swordman, pikeman, clubmen, axeman. So basicaly your unit starts off with "no armor" just a shield and weapon... and then you decide which ones you want to give which units, at a loss of speed...
your gear or "kit" wouldnt look different as you ranked up... instead if you got a tech it would change the appearance of gear.
I am rather fond of techs. In fact, i recommend to check this mod for unit specific upgrades. I think it is a great way to differentiate civs. Some civs may need to research some upgrades, some civs could have the upgrade for free, some civs could be missing some completely.