Please tell me I'm over-thinking this!

You're over thinking this! :) Or rather, going about things the hard way.

Assuming the command you gave does what you need everywhere bar Windows, just use this when you detect Windows:

system qq[ for /d %d in ($tmp\\scale-*) do @rd /q /s %d ];
[download]

Eg:

C:\test>dir /b /s ppp
C:\test\ppp\donttouch
C:\test\ppp\scale-123
C:\test\ppp\scale-124
C:\test\ppp\scale-125
C:\test\ppp\donttouch\junk.1
C:\test\ppp\scale-123\junk
C:\test\ppp\scale-123\junk\junk.1
C:\test\ppp\scale-123\junk\junk.2
C:\test\ppp\scale-123\junk\junk.3
C:\test\ppp\scale-124\junk
C:\test\ppp\scale-124\junk\junk.1
C:\test\ppp\scale-124\junk\junk.2
C:\test\ppp\scale-124\junk\junk.3
C:\test\ppp\scale-125\junk
C:\test\ppp\scale-125\junk\junk.1
C:\test\ppp\scale-125\junk\junk.2
C:\test\ppp\scale-125\junk\junk.3

C:\test>for /d %d in (ppp\scale-*) do rd /q /s %d

C:\test>rd /q /s ppp\scale-123

C:\test>rd /q /s ppp\scale-124

C:\test>rd /q /s ppp\scale-125

C:\test>dir /b /s ppp
C:\test\ppp\donttouch
C:\test\ppp\donttouch\junk.1
[download]

Why reinvent an operation that the OS already knows how to do?