i dont know when did u look at the motherboard cpu compatibility but i checked right now in it does list the 2700x to so duble check
When I copied the info from MSI Support on your Motherboard, the Ryzen 7 2700x wasn't listed. But as you mentioned IT IS LISTED today. It uses the same BIOS (03/2018) as the Ryzen 7 2700 CPU which is the latest BIOS update.
Here is the new listing from MSI Support for CPU compatibility with your B350 Tomahawk Motherboard:
RYZEN 7 Pinnacle Ridge YD270XBGM88AF 2700X 100 3.7 4M 16M B2 105 N/A 7A34v1G.zip RYZEN 7 Pinnacle Ridge YD2700BBM88AF 2700 100 3.2 4M 16M B2 65 N/A 7A34v1G.zip RYZEN 5 Pinnacle Ridge YD260XBCM6IAF 2600X 100 3.6 3M 16M B2 95 N/A 7A34v1G.zip RYZEN 5 Pinnacle Ridge YD2600BBM6IAF 2600 100 3.4 3M 16M B2 65 N/A 7A34v1G.zip
EDIT: Deleted my previous post since they updated the CPU Compatibility List on MSI Support for the B350 Tomahawk Motherboard.