Base Mac mini still has slower storage than any other configuration

The 256GB configuration of the new M6 and M5 Pro Mac mini features storage that's around half the speed of that in other models, although it's still faster than the previous generation.
M4 Mac mini review
The greater disappointment with the New Mac mini is that it no longer has a slotted SSD, meaning it's not even theoretically possible to upgrade the storage as it was before. But now new benchmark testing by Japanese technology site AAPL Ch has revealed that Apple's SSD is slower in some config