Having multiple threads does not mean that they are all doing equally useful work. Single threaded performance is absolutely critical for a desktop machine.
Even in multithreaded desktop applications, it's rare to see them effectively use more than 8 threads.
There are some tasks where single core definitely limits the performance (some games especially). For most of the 'compute' oriented tasks like CAD/3D, LLMs, etc. multicore is great, and the slow single core speed doesn't seem to get in the way.
I would still rather have 128 M1-class cores than 128 Neoverse-N1 cores :)
macOS, ChromeOS, Windows and Android are heavily multithreaded, even when there is one main application thread, the underlying OS APIs are using auxiliary threads.
Even in multithreaded desktop applications, it's rare to see them effectively use more than 8 threads.