If restarting Studio fails to resolve the issue, try rebooting your machine.
Just had this happen to me, restarting Studio, which normally fixes the issue failed.
Rebooting my laptop fixed the issue.
Studio Version.
InterSystems Studio Client 2022.1.3 Build 670 Patch 1
Server IRIS for Windows (x86-64) 2022.1.3 (Build 668U)
You could write your own std deviation ClassMethod() in ObjectScript. You then have the flexibility to use that however you want.
The logic doesn't look that complex, and for a few thousand rows would run fast enough in Object Script.
See link below for the calculations you need to do:
https://www.scribbr.com/statistics/standard-deviation/
You can validate your results with the STDDEV(SQL) method, which will also allow you to compare performance.
I don't see why you can't create another ClassMethod to test GetAllRecords()
Your test ClassMethod would need to create instances of %CSP.Request and %CSP.Response and set any properties required but it should be possible.
Looking at the Documentation for %CSP.Request it actually mentions the Command Line:
http://cg-az-cendev01/csp/documatic/%25CSP.Documatic.cls
property CSPGatewayRequest as %Boolean [ InitialExpression = 0 ];