Surface book 2 15 inch 256G super low wirte speed

My surface book 2 (15 inch, i7, 16G, 256G ssd) shows high read speed (~3000 mb/s), but super low write speed (~330 mb/s).  I returned my 1st one due to this super low write speed, but 2nd one also show almost same benchmark speed. Based on other reviews, these numbers are consistently reported in 256G ssd model. I wonder if this write speed is normal or it can be improved by firmware update later. If this write speed is normal...why MS used this ssd?. 300mb/s write speed is much slower than my 2yr old surface pro 4 256G (~1000mb/s) and 3yr old 256G ssd(~800mb/s) in my desktop....