As noted often, the market for SSDs has a case of a 'race to the bottom' and a 'race to the top' at the same time. With regular SSDs the emphasis lies on lowering the production costs as much as possible in order to be able to offer these products at a lower price. By now the performance is secundary: if a product performs well with regular use, the manufacturer is often happy with the product.
The race for the highest speed shifted to the terrain of the PCI-Express SSDs where the limitations for SATA-models and the AHCI-protocol no longer apply. There are only a few manufacturers that tried releasing mid segment or budget PCI-Express SSDs.
In case you do not remember: for a long time the performance was limited to around 500 MB/sec, because of the limited bandwidth of the SATA600 bus. The use of newer interfaces was necessary in order to achieve higher speeds. For this PCI-Express and NVMe can be used, but more on that later.
The performance of SATA-SSDs has not been exciting for some time now.
Intel was the first to succeed in releasing PCI-Express SSDs for consumers. They did this by releasing their products developed for use in servers in a slightly different form (for example, flash memory was no longer SLC but MLC). The performance of this Intel 750 SSD was extremely good, but it was also very expensive and it consumed a lot of power.
Samsung was the first manufacturer that released PCI-Express SSDs truly developed for consumers. This was the 950 Pro series that was released in October 2015. There was a PCI-Express SSD of the company available for OEMs for some time, namely the SM951. Through detours this drive was available in webshops as well. The difference between the 950 Pro and the SM951 was the used flash memory: the 950 Pro had 32-layer 3D NAND, compared with the 16nm planar flash memory of the SM - they were identical in every other regard, also in terms of the used controller.
After this Samsung remained quiet for some time. The expected 950 Pro 1TB was never released, and the 48-layer 3D NAND memory took some time. Slowly but surely other manufacturers also released PCI-Express SSDs, with controllers such as the Phison PS5007. In contrast to Samsung's preference for M.2, they often released their products in the form of a PCI-Express insertion card. Plextor, Toshiba (under the sub brand OCZ) and Zotac entered the market as well as other manufacturers, but they were never able to gain a substantial market share.