So let's start saying this: I'm totally fine if old lore characters die (as long as they die in a meaningful way for the story), and new characters come up.
We cannot negate that every expansion new characters get developed. Garrosh was the main example of this, wheter you liked how that story went or not, he was developed in 3 expansion from WotLK to MoP.
Looking at more recent years we had people like Khadgar, Gul'Dan, and now we have or example Genn Greymane, Odyn, Maiev, Thalyssra and so on.
That's great.
The problem here is that many of these characters do not carry over that much in future expansion, or at least that's what happened until now. We definetly saw a change in style between WoD and Legion, where the story continue in a nice flow and the characters can transition.
But it wasn't the case before. This is painfully obvious if you look how the racial leaders of the horde are right now.
Vol'Jin died like a clown before he could show us anything, and now the trolls are in shits creek. No personality or charismatic dudes to rapresent them. Cairne Bloodhoof died back 4 expansion ago and we got this other clown of Baine who did literally 0 in 4 expansions. Thrall shaved his head and went out to do god knows what, garrosh is dead, vol'jin comes, he is dead, now we got Saurfang that is meh. We saw very little of him and he is leading the orcs.
What i'm trying to say that there are many examples of this type where you can jsut say blizz is fucking up somewhere because we are losing more and more old lore personalities, basically the dudes the define the word "Warcraft" but we aren't getting as much new charismatic characters to replace them.
That is my feeling right now and i hope that they know this is a problem