If a game uses 8 core than it uses 8c if not then it is not. Which game? Not all of them are the same. You make it sound like a game chooses by itself whether it wants to use 8c or less. It is not the game, it is the developers to decide.
None of this is correct.
Programs don't "use cores". They don't even see cores.
Programs just send instructions, which the OS and CPU try to run as fast as possible.
Any program can be run on a single core. Even if a program can use 8 or 16 or million threads, it can be executed on a single core - returning the exact same result.
We make multi-core CPUs not because that's better, but because the cores we can make aren't fast enough for our needs.
To utilize many cores, a program must be able to run parallel threads.
Sometimes it's very easy because the problem is perfectly parallel (like adding long vectors) and you can use every core available.
Sometimes it's hard because the problem isn't parallel. And
games, as a whole, aren't parallel.
Every game is fundamentally a sequential program, because it has
a timeline. Games played by humans are interactive and even more limited.
There's no magical variable USE_CORES=8 that many people on this forum believe in (also suspecting that Intel bribes game studios to set it low).
You have to "chop" the program into parts that can be run separately.
For example: one thread loads maps, one does the AI, one feeds the GPU, one communicates with the server and so on.
And even if you manage to "chop" the game into N parts, it'll still run on any number of cores smaller than N.
So the answer is "no". No game NEEDS 8 cores. No software NEEDS 8 cores. At best, they may be able to UTILIZE 8 cores, which is something entirely different.
Of course you do :-D
Recently built a 2920X based system that not only benchmarked well in power user tasks but also gaming.
Name 3 "power user tasks" that you've benchmarked. I'm honestly curious.