In essence,What is the difference between Nathanos and Nazgrim？

[Ardenaso]

He only stuck with Garrosh out of pride, and perhaps out of self loathing, feeling he couldn't be forgiven and had no place in Thrall's honorable Horde. He was an old soldier who wanted to die in combat.

we need more Warcraft characters like this, too many cliche "your victory means nothing" characters

[XalAtoh]

Naz'grim loyal to the Warchief.

Nathanos is just a simp, he would roll in a mud if he can make good looking strong lady say "you are kinda funny".

[Combatbutler]

One is loyal to a rank no matter what, the other to a person.

[Skayth]

Nazgrim is loyal to the horde and warchief. Honor and loyalty holds him bound, hence why he is a tragic character.
Nathanos is a simp for sylvannas, and sylvannas only. Thats it

[Zulkhan]

Nazgrim was misguided and dumb, Nathanos is just a fuckboy.