An 8 GB Mac is not a 16 GB with defective RAM; it literally only has 8 GB. The RAM is separate dies and Apple presumably buys known good DRAM so the yield isn't their problem.
Both the memory controllers and RAM on the Mx are on die components. The number of controllers (binned) count here. I should have been more specific in what I was saying.
"The 14-core M3 Max only enables 24 out of the 32 controllers, therefore it has 300 GB/sec vs. the 400 GB/sec for all models of the M1 and M2 Max, while the 16-core M3 Max has the same 400 GB/sec as the prior M1 and M2 Max models."
FWIW, almost every x86 computer made in the past 10 years has an on-die memory controller. The only exception is a handful of decade-old machines with "Northbridge" chips inside.
