According to tests conducted by 9to5Mac, the SSD on the entry-level 14-inch M2 MacBook Pro is slower than its predecessor.
In BlackMagic's Disk Speed Test, the 512GB SSD in Apple's current flagship achieved read speeds of approximately 2,970 MB/s and write speeds of approximately 3,150 MB/s, whereas the M1 Pro with a 512GB SSD was capable of 4,900 MB/s reads and 3,950 MB/s writes.
This indicates that the 2023 base model has around 39 percent slower reads and 20 percent slower writes compared to the 2021 model.
The difference is presumably attributable to chips. According to 9to5Mac, the 512GB SSD in the previous-generation 14-inch model has four NAND storage chips, however the SSD in the M2 Pro appears to have only two.
Those are plainly higher-capacity chips, so although the computers have the same amount of storage, their performance is diminished since they cannot parallelize reads and writes as efficiently.