use robocopy for data

steam/build.bat

@@ -1,7 +1,7 @@
 @echo off
 mkdir content
 xcopy /I /D /Y /S "..\x64\Release\*.dll" content
-xcopy /I /D /Y /S "..\data\*" content\data\
+robocopy "..\data\" "content\data\" /MIR
 for /f %%i in ('git rev-parse --abbrev-ref HEAD') do set BRANCH=%%i
 for /f %%i in ('git log "--pretty=format:%%h" -n 1') do set HASH=%%i
 for /f %%i in ('git rev-list --count HEAD') do set COUNT=%%i