It's true that trends and stagnation can be harmful to an industry. Just look at the isekai genre of light novels and manga. But in that example, isekai is practically cannibalizing every other genre in its wake. Other games are still in a marketable state and we aren't seeing waves of people saying that they now refuse to play any video games that aren't like Dark Souls.

The Souls genre of video games is also a fairly challenging style to get down properly while still adding some touch to make you stand out. As long as it doesn't become like the Clash of Clans situation where everybody tries to steal the game's heart and soul along with its structure, I think the industry will be fine.