Yes, that's what I meant by "Mainstream DRAM". The basic parameters are specified by standards like JEDEC, so the most common types can be used in many systems thus reach high volumes. This can be less true for specialized RAM like HBM or the highest performance grades.
Is it fair to conclude that DRAM is basically a commodity that can be specified well enough by a set of parameters?
If so it won’t allow you to get any competitive advantage in your products and thus wouldn’t be a business you want to be in as Apple.