I am on Chapter 31 of the manhwa, and the story feels if it's the amalgamation of the three manhwa in order from left to right:-
[Damn Reincarnation]
In both stories, the protagonist was a legendary warrior from a past era who fought against great evils. Both are reborn/reincarnated into a future where their past exploits are now history or myth.
[The Archmage Returns After 4000 Years]
Both protagonists are ancient beings who return to a world that has "degraded" in terms of magical or combat prowess. They both enter academies where the instructors are significantly weaker than they are.
[Necromancer Academy and the Genius Summoner]
Both protagonists have parents who were legendary figures in the academy. The academy is also similar in the fact that the academy is supposed to be for the best the continent has to offer, but the students seem to be ordinary except for a few, and many professors seem to be counterparts of the other manhwa