I cant comment on the multithreading capabilities of excel formula calculations but the problem with excel formulas is they are continuously recalculated unconditionally whenever worksheets are refreshed. There are 6 worksheet refreshes per bet angel worksheet per guardian cycle. 7 refreshes per cycle if you have opted for optional values like VWAP.
VBA code can be developed so that calculations are performed conditionally so that numbers are only crunched when actually needed. So my code would typically be something like if the market volume has changed then crunch numbers selectively via VBA else dont bother. Excel formula would be blindly recalculated needlessly on every refresh. In my experience multi sheet workbooks with lots of formula are slow while well optimised VBA calculations are much faster.