You're pretty far off the mark about SSD caching. A majority of consumer SSDs are now DRAMless, and still can exceed PCIe 4.0 x4 bandwidth for sequential transfers. Only a seriously outdated SSD would still be using DDR3; good ones should be using LPDDR4 or maybe DDR4. And when a SSD does have DRAM, it isn't there for the sake of caching your data, it's for caching the driver's internal metadata that tracks the mapping of logical block addresses to physical NAND flash pages.

Here’s a page comparison 8 modern SSD cache, notice how they all fall off once the cache is full.

https://pcpartpicker.com/forums/topic/423337-animated-graphs...