Honestly, possibly because of my Silicon Valley biases, I tend to think that the idea isn't sacred, it's that the execution on the idea is what turns a good idea into a successful one, and Epic executed way better despite PUBG's initial momentum. They threw it away with performance problems, bugs, cheaters, etc. and Fortnite capitalized.
1. You are still given a monopoly over selling your game, and someone else can't just make the same game using your assets, so at least you get to make money from your work via copyright.
2. It's a game, so I would argue that it's not worth as much to society to let you monopolize selling of a game mechanic as opposed to, say, a mechanical design. (I'm fully aware of patent controversies, but we're talking about games so I'm staying at broad strokes.)
3. I think there's an argument to be made that games are more like art than machines, and thus they count enough as speech that over-protecting IP rights in games would have a chilling effect.
Just some thoughts.
Nothing is completely novel, or original. Everything made today is built on our collective experience up to the moment we release it. Its why you can't patent a concept like "battle royale" or "arena shooter" or "survival game" the same way the first successful action movie couldn't patent action movies.
Arguably I feel like the idea is too simple to deserve any kind of protection. It would be like protecting "hide and seek" or "tag"
Trying to block or interfere with this, like IP laws tend to do these days, will cause stagnation and break the main reason why free market has proven to be the most people-serving economic system.
Doom clones? (first person shooters)
Warcraft clones? (real time strategy)
...
Staying on the gaming topic, you could say Call of Duty is a copy of Counter Strike? I'm not sure which came first but the idea still stands.
You can start a death match in Unreal Tournament 2004 and check some settings to make it a sort of battle royale.