A common theme in LitRPG is that the "old monsters" who are at the top have watched generation after generation of prodigies be birthed, rise to moderate power and then either die or stall out and become irrelevant. Something that DotF kind of touches on is Zac going through this, but I think it could be more pronounced. We know that Zac isn't going to die or have his growth halted before he concludes various plotlines, but we don't know who is going to make it through any given arc. There are so many secondary/tertiary characters, letting several die or plateau (and then die like Sap Trang) would be fine and would increase the stakes.
This is a problem I have in a lot of long-running fiction though. After a certain point, likable characters around the lead character are immortal.