A lot of Pre-Third War Quel’Thalas’ culture was based in bloodlines and nobility. For example, the position of Ranger-General was hereditary, passed down through the Windrunner line over the generations. While the Windrunner’s trained their successors to be the best, the fact is, the next Ranger-General would always be a Windrunner. So, even if there was someone better, they wouldn’t be the Ranger-General.
By contrast, modern Blood Elf society has abandoned the concept of bloodlines being the deciding factor in how they are run. They’re a meritocracy now, where the best, the brightest, and the strongest rise to prominence. You need only look at Astalor Bloodsworn’s failed apprentice back in WoD to get an idea of this. He dismisses her as being good for nothing more than mere basketweaving, and goes on to say that, as he doesn’t associate with basketweavers, she should clear her desk out.
Tying into this is where ambition has become a cornerstone of Sin’dorei culture and identity, whereas in old Quel’Thalas, such qualities were deemed unseemly; a magister learned and rose on their own time, and to hurry to power was undignified, like some short-lived human grasping for as much magic as they could before their tiny lifespans were spent.
Mind you, this isn’t to say modern High Elves really embody that old culture, either. As they’re largely made up of elves whom left Quel’Thalas before the Third War, they were outliers to what would’ve been considered normal back then as well. Old Quel’Thalas’ culture is dead and gone at this point.
