Sure, a poweruser can bring their own ram/ssd. But again they pay almost as much and have a worse system performance wise.

Normal users don't profit from anything you listed. They do have to buy a notebook with all components, and thus currently have to pay more for linux/windows hardware compared to Apple.

Also, RAM isn't backwards compatiple. Literally had this problem with my old ddr4 not fitting in the newer ddr5 slots when my ddr5 acted up.