Yes, their culture changed
True, but an Italian, a Roman, a Turk , a Greek, an Englishman and a German is a Human ! Like how a “Black”, a “White”, a “Red”, or “Yellow” one is a Human even tho’ their look ,skin color and culture and even language are different
The Draenei suddenly not changed their biology when left Argus, nor the Lightforged. True, the Man’ari are changed a lot, due the Fel and Demonic influence, and some of them became Demons, but not all.
Good example for this the Orcs
Is a Mag’har an Orc? Yes. Yes they are
Are the “greenskins” who drank Mannoroth’s blood and got tainted by Fel are Orcs? Yes
Even the Red Orcs/Fel orcs are Orcs
Like how we call the Kaldorei, Shal’dorei, Quel’dorei, Sin’dorei Elves. They are Elves. And they changed way more that the Draenei, the “exiled Ones” changed after they left Argus or the Lightforged
Eredar is the race name, all the others are as you said, names of the groups with different culture
We not really stopped calling Germans Humans after the II. World War or their victims left behind the Human racial name, yet they (not all, especially not the populace - let’s not drag that one in to this) did some nasty things, like the Man’ari “unnatural” Eredars in the service of the Legion.
Actually, what effects? The Draenei changed their culture to be a Light-centered “cult” and started worship the Naaru and adopted some of their technology. And the Man’ari became mostly red skinned (not all, Archimonde for example) or grew wings. The Lightforged gained cool metal tattoos.
How many generations was born and raised since they left Argus?
We don’t know
But we DO know, lots of the Draenei/Lightforged are from Argus, from pre-Sargeras era (enough NPC around, like that mushroom vendor on Draenor, etc) and they not changed (the ghosts and even the language of the pre-Sargeras times Eredar are quite a proof of this) and looks like the new generation of Draenei kids running around
Presonally I think its a great source of RP how one tries to distance himself from the deeds of his people to a point even trying to proove, we are not related, please don’t mind the Man’ari who was the son on our ‘Draenei’ Prophet - OR try to reconnect with his past he had to left behind when was forced to flee his planet and desperatly tries to clean the Eredar name that once was respected in the Great Dark Beyond but was befouled the man’ari