Kalran: Tales of the four nations/Veterancy

As units fight in battle they will earn experience, passively in small trickles and in larger amounts when damaging enemies and taking damage. Experience is mainly used to gain points to purchase protocol but is also used to upgrade their units into veterans, depending on the faction.

Earthborn (Dwarves, Fenrir, Xiagui, Goliath), ADF, and Ouroboros
Playing similarly to command and conquer and company of heroes. Individual units gains a rank as they gain experience, buffing their stats while granting them special bonuses. But ranks are given per individual, meaning its a long process to level every base unit to a veteran, and if a veteran unit dies they take that veterancy with them.

Waterborn (Humans), Byzalem, and Asura
Based off the British from company of heroes. Only officer units gains veterancy, and any experience a unit gains will be transferred to the nearest officer. Said officer in turn grants an aura, territorial, or global buff to units and unlocks special passives. But officer units are more expensive then other units and, while produced instantly, are locked behind cooldown. Meaning that its hard to mass multiple officer units

Fireborn (Orcs, Rokhari, Salamander, Mukasura), Guilds, and Horde
Based of the Wehrmacht from company of heroes. Veterancy is purchased through their hq, costing both resources and experience, which is then applied to all new and existing units. Making each of their units stronger while not suffering much setbacks when such units are lost compared to losing an officer unit or a veteran.

Windborn (Elves, Navaheim, Nekomata, Faunus), Tenko, and Reclaimers
Playing more closer to classic and blizzard RTS. Their units can't gain veterency. Instead experience is used to purchase powerful upgrades, which cost a lot of experience but are done instantly, more powerful units, and to unlock and use more powerful protocols