The core mechanics of Diablo also haven't truly "evolved" that much throughout the series. Both game franchises are about fighting hordes of enemies at a high speed with a combination of standard attacks and special abilities. Dynasty Warriors features dozens of uniquely animated playable characters to Diablo's small handful, and while they do sometimes re-use assets for their expansion packs or compilation crossover games, they just as often fully refresh them. And all of the licensed games have completely unique assets.

Calling something a re-skin is a weird insult to the artists and animators that have to craft new characters for each new game. Yes, they're all hack and slash action games at the core, but if Hyrule Warriors is "just a re-skin" of Dynasty Warriors in spite of having new levels, animations, moves, items, sounds, music, and dialogue...then Diablo 3 was simply a "re-skin" of Diablo 2.

I agree that Path of Exile is an exceptional game with a large and deserved following, but that hasn't stopped dozens of other studios from releasing quality successful competitors without fear. The Torchlight series, Borderlands 3, Wolcen, Grim Dawn, Victor Vran, and many others have all come out with prices attached and found a following. Free games like Genshin Impact, Black Desert, Warframe, Dauntless, and Phantasy Star Online 2 have also done well.

If Blizzard is truly so afraid of POE, and Activision is afraid of putting money into "non-monetized" games....then they wouldn't have three new Diablo games in active development. And at least two of those will likely be heavily monetized with Immortal and IV. The more time and money they spend making Diablo IV, the more they'll need to recoup later.

Blizzard's biggest problem is themselves.