First of all, the 9900k doesn't cost half the money. Second, you can also buy a 3900x if you want 12 threads with similar ST characteristics and pricing closer to the 9900k. There are other options.

If you want to game @ 1080p and do mostly single threaded work (without parallelism), this CPU is not for you. If do a lot of single-threaded jobs in parallel (for example, gaming + being a server or gaming and streaming) or anything multi-threaded, this CPU destroys the 9900k, while being just a bit weaker when doing just one or two single-threaded tasks.