However, Amdahl's law means that serial/single-threaded performance remains an important determinant of total performance even in multi-threaded applications. Locking is a great example, even in a heavily multithreaded program you can be limited by lock contention, that specific part of the program is serial.
Gustafson's Law is of course a thing, eventually we will come up with additional work to fill those cores, but single-threaded performance remains a critical factor for CPU performance.
Most of the time we don't get to choose which software we run. Hell, most core components of Windows get stuck in a single core still. I'll take single-core performance over multi-core performance any day. Maybe that will change in 10 years, but I live in the present.
If your workloads are limited by single thread performance you need better software. It's why vulkan and dx12 are a thing. (The single thread limitation of committing a frame to the GPU has been reduced by an order of magnitude) It's why C++ has the parallel algorithms library baked into the language.
I get it, threading is hard. But it's honestly not that hard. It's only hard when you're maintaining some super old program with single threadedness engineered into its core architecture. (note: this is my day job) Greenfield applications since 2009 should have had threading built in as a core assumption.
AMD is doing the right thing by optimizing for multithread performance over single thread performance. Moore's Law is dead for single cores. It has been for a decade and a half.