A quick look inside the entry-level MacBook Pro M2 Pro reveals something I didn't expect to see – or rather, something I SHOULD have expected to see is missing. Like the baseline M2 MacBook Air, the baseline of the latest 14″ The MacBook Pro appears to have fewer NAND chips and more storage capacity than the previous generation. This causes the read and write performance of the SSD to be significantly lower than the previous generation.
The base models M1 and M2 MacBook Air have only 256 GB of storage space. In the MacBook Air M1, this storage was split between two 128GB Kioxia NAND chips. When Apple moved to the M2, they switched to newer NAND chips that provided 256GB of storage per chip. This meant that the base model M2 MacBook Air, with only 256GB of storage, had only one NAND chip, and the performance of the SSD was affected as a result.
Like the M1 Air, the M1 Pro, with a base capacity of 512 GB, was split between four 128 GB NAND chips. In the iFixit teardown, they show two 128GB NAND chips on one side of the board and two more 128GB NAND chips on the other side. Like the M2 Air before it, the M2 MacBook Pro appears to have switched to larger NAND chips, leaving the base model with slower SSD performance.
M1 Pro MacBook Pro 512GB 
M2 Pro MacBook Pro 512GB
Given the noticeably slower SSD performance in my M2 Pro MacBook Pro, I wanted to look inside to see why. Of course, while the MacBook Pro M1 Pro 512GB had two NAND chips visible on the front of the motherboard and two more on the back, the MacBook Pro M2 Pro only had one visible on the front of the board. There is probably a second NAND chip directly countering this, like the M1.
While higher NAND storage density is good, it's always a pain when a product gets worse between generations. Luckily, most people won't notice the impact of this in everyday use. The read and write speeds of the drive are still extremely fast, so the difference is likely to be noticeable only in extreme cases.
