With the release of ArcGIS Pro 2.1 came several new tools, one such tool is the Calculate Fields. I assume there are improved performance benefits using this tool when doing multiple calculates in a table (as opposed to sequential Field Calculates called on a table).
The problem is that this tool is practically useless as it does not allow you to build up the expression, it is simply a text box which you type into. The whole idea of running calculates on many fields would imply different calculations and thus different expressions. It is essential to have the expression builder interface as you get in the Field Calculate tool.
Unless you are going to apply simple constants to each field I can't see anyone adopting this tool as one needs an expression builder like interface to construct complex expressions.