In 2016, Intel released the Core i7-7700K, a 4-core, 8-thread processor, running at a base clock of 4.2 GHz, with a maximum turbo clock of 4.5 GHz, selling for USD 350.
Now, in 2018, the equivalent to that would be the Core i7-9700K, an 8-core, 8-thread processor, running at a base clock of 3.6 GHz, with a maximum turbo clock of 4.9 GHz, also selling for USD 350.
Intel is doubling the number of cores, but keeping the same number of threads. While the base clock is lower, the turbo clock is higher. But then it's a 2-year difference between them.
The Core i9-9900K has 8 cores and 16 threads, but it is not a successor to the i7-7700K. It is a new product, in a new segment, which Intel is creating to be able to charge more (USD 450).
What I did not see in the new line-up is a successor to the i7-7700 and the i7-8700. The higher "non-K" processor would be the i5-9600, and I have not seen an i7-9700. The leaked line-up may be incomplete, or Intel may have chosen to intentionally scrap the "non-K" i7, to be able to compel consumers wishing for a higher core count to jump into the more expensive i7-9700K instead.