Well, yea, SATA is 6Gb/s versus USB 3.0's 5Gb/s, so yes, SATA can be faster. You would need to turn the SATA connector into an eSATA connector but that's not too difficult.
I am aware that there are cards that allow you to use M.2 connectors for other things, but the NUC BIOSs do not have support for handling these cards. The BIOS expects a WLAN card in the M.2 Type E connector and a SATA or NVMe SSD in the M.2 Type M connector. Anything beyond that is considered unsupported. Now, I am carefully saying just 'unsupported', there is always a chance that they might work; I just haven't tried.
Wait a minute, that's not completely true. It is something that attempts to utilize the PCIe lanes in the connector that is the unknown. I do know that there are cards that will allow you to gain access to the second SATA port that is carried in the the M.2 Type M connector. In fact, I actually have one of these cards and have used it to connect a 3.5" SATA drive outside the chassis. Here is the one that I have: https://www.amazon.com/gp/product/B07G2YXLFP. Using this, you could have two SATA ports that you can cable out of the chassis.
...S
