I think that's the whole point - it may not have been a deal breaker, but nothing in the Mac line up is cheap enough to warrant that kind of corner-cutting. Apple don't make cheap laptops for doing email and updating your Facebook page. You can do that with a $200 Chromebook, or a low-end iPad - even a MBA is potentially capable of a lot more, and that's reflected in the price.Obviously for the price of these machines you don't want any compromises and I get that. But realistically...I didn't buy into the SSD speed boogeyman.
The machine was designed to have a dual-channel SSD, previous incarnations did have a dual-channel SSD - we're not talking about a 'future expansion' slot here – and the M2 Air wasn't even launched as the "entry level" MBA - that was the $999 M1 MBA. Anyway, we're talking about the cost price difference between 1x256 GB chip plus. 2x128 GB chips plus the marginal cost of soldering 1 more chip during a highly automated construction process. This really was penny pinching.
Why they did this in the first place is unknown - possibly the 128GB chips were affected by the great chip famine of '22, and/or maybe 2 x 128GB ended up costing more than 1x256 because the demand for such small chips was falling & production was ramping down... Of course, that is partly because 256GB is becoming increasingly small beer, and we're long past the point where 512GB should have become the minimum on a $1200 premium laptop.