Ni No Kuni 2?
You run and grow a kingdom and get in skirmishes where you control an army that you can upgrade. Upgrading buildings gets a you visual difference as well and new gameplay mechanics and skills.

Divinity: Dragon Commander - Title speaks for itself.

In the Baldur's Gate and Icewind Dale series, you can choose your whole party of 6 adventurers, and give each adventurer a different build (Ranger/Rogue/Paladin, etc.).
Does that fit the bill?

I am not sure if you want units that evolve over time, or also units that transform back and forth during specific times.

For the latter, I can cite some nice JRPGs (anime warning! :D):

1. Tales of Zestiria has mechanics where during battle two characters can merge to form a new, more powerful, character (I would imagine many of the "Tales" RPGs have this mechanics, maybe?).

2. Similarly, each party member in the Neptunia games I played can transform mid-battle after accumulating enough "energy" of some sort.

These transformations are visible in the trailers, so see if any of these rocks your boat.

You should check out Symphony of War, definitely seems to hit most of the checklist that you want, tons of units that can you promote(they do change their looks etc)/equip items and the like.

Maybe not exactly what you are looking for, but Wildermyth might be worth a look. In addition to classes and upgrading skills and gear, your characters can pick up various transformations that let them evolve into powerful beings over time (like a werewolf, spirit bear, fire elemental, etc). It's even possible get aspects from multiple transformations on the same character. Transformations are persistent across playthroughs, too, so you can continue developing a character across stories. It's kinda rng dependent, though, so it can take a bit of luck if you are aiming for a specific build.

Try valkyria chronicles( 1 and 4 are for pc),tales of series or legend of heroes series

Siralim
Heroes of Might & Magic III
Geneforge
Dominions 5

Heroes of Might and Magic 5 with its expansions allow you to choose from two types of upgraded units, usually with a different aspect of them being in focus. Skeleton -> shielded tankier skeleton / skeleton archer. Though in many cases one upg. is clearly better than the other.

The Might and Magic games let you control a party and adventurers, and you can spend time, money and energy on their individual skills, with quests to master an ability afaik. Mastering magic branches is an option, and at least in one of them you can turn your spellcaster into a lich . I don't know how much personal change and specialization exists for others.

Dawn of Magic 2 is an antion-RPG that is single-player and I'm not sure if it features a party. But as you learn new and new magic skills, they also physically change the looks of the character.