The 2019 MacBook Air released last week has a slower SSD than the 2018 MacBook Air. The 128GB and 256GB models were tested (via Consomac).
2019 MacBook Air
Using the Blackmagic Disk Speed test, the read speeds of the SSD are slower. It found write speeds of 1GB/s and read speeds of 1.3GB/s. Meanwhile the 2018 MacBook Air had write speeds of 920MB/s and read speeds of 2GB/s.
The read and write speeds of the 128GB model were similar to 2018’s equivalent model, with write speeds of 500MB/s and read speeds of 1.3GB/s. Models with higher capacity SSDs weren’t tested. The slower speeds could be a result of Apple lowering the price of the 2019 MacBook Air.