TYPO3 Core

Should it not be:

page.200.value = {$myConstant}

data expects some functions (see https://docs.typo3.org/m/typo3/reference-typoscript/main/en-us/Functions/Data.html) as input while a constant is not part of that.

I think the issue here is rather that the processing from the data type Data/getText is not consistent.

According the documentation the content from curly braces in the property dataWrap is treated as type Data/getText. Since the property data is of the same type the same result is expected... From the docs:

Regarding data: Data type: Data / getText / stdWrap

Regarding dataWrap: The content is parsed for pairs of curly braces. The content of the curly braces is of the type Data / getText and is substituted with the result of Data / getText.