Yeah but DDR3 was faster then and still is now - I can't imagine my M4 Mac having a slightly older version RAM would meaningfully affect me, but another 24GB of it (or whatever I have) would certainly be an improvement.

CPUs have L1, L2, L3+ caches too after all.

A better SSD can get up to a passable GB/s rate, but when you're waiting tens of microseconds instead of tens of nanoseconds you can't use it the same way. And a worse SSD is 10x slower in GB/s too, compared to old super cheap RAM.