That leaves about 1B transistors for each of the 12 cores (6 CPU + 6 GPU). The instruction set is a few hundred instructions. Surely it doesn't take millions of transistors to implement each instruction. Other than the cache, which parts of the processor need millions of transistors?
I've heard the cache is the biggest part. Per https://en.wikipedia.org/wiki/Apple_A17, the A17 has 72MB of cache. Cache is typically SRAM. Per https://en.wikipedia.org/wiki/Static_random-access_memory, a single bit of SRAM typically uses 6 transistors, but it could be anywhere from 4 to 10. So that's between 2.3B and 5.7B transistors for the cache.
That leaves about 1B transistors for each of the 12 cores (6 CPU + 6 GPU). The instruction set is a few hundred instructions. Surely it doesn't take millions of transistors to implement each instruction. Other than the cache, which parts of the processor need millions of transistors?