Looking at this from 30,000 ft:
Sure, Apple doesn't spec performance at all, nor provide any guarantee as to what SSD might be used inside the Macbook Pro. Also, no way to know from the product number or serial number as to what components may be found inside.
You would think that Apple would have multiple sources that would deliver similar performance.
ON a related note, Apple does offer different, identifiable graphics options: display resolution and type of graphics controller.
Back when Apple provided internal HDD, they used different manufacturers and sometimes spec'ed the rotational speed. Unfortunately, rotational speed alone did not guarantee a particular level of performance as some generations of 5400/5900 RPM drives could deliver faster throughput than a 7200 RPM drive. Rotational speed only determines latency. Similarly, different drives could have different cache sizes, too, which affected performance.
So is the OP overreacting? Perhaps a little, but if he is not happy because he is not seeing performance that others are experiencing, he is within his rights to return for a refund or exchange. He would have some extra leverage if he paid using a credit card that has a benefit permitting refunds for any reason.
The comment about Sandisk SSD vs Samsung is also of interest.
So is 100MB/sec performance difference important? Depends on how the computer is used. Look at those green checkmarks below the speed dials. Appearance of more "x" characters would indicate an inability to do editing for certain resolutions using certain video formats.