No CALCULATE Challenge -- Round #2b

 inside a measure, 

Note that measures implicitly use CALCULATE, somewhat negating your premise.

Having said that, try this version

DONCB = 
VAR b = ADDCOLUMNS(ALL(Geography[RegionCountryName]),"do", [Distinct Orders])
RETURN SUMX(FILTER(b,[RegionCountryName]<>"China"),[do])

AlexisOlson 
Here is a solution using SUMMARIZECOLUMNS.

Distinct Orders (Non-China Benchmark) TJ = 
COUNTROWS (
    SUMMARIZECOLUMNS ( Sales[OrderKey], 
        FILTER ( 
            ALL ( Geography[RegionCountryName] ),
            Geography[RegionCountryName] <> "China" 
        ),
        "@Count", COUNTROWS ( Sales )
    )
)

However, applying the same filter over a higher cardinality column will reveal the difference with the SUMX solution provided by lbendlin . DISTINCTCOUNT is non-additive calculation, which means SUMX will result in wrong results.