I understand that the workaround could be -(10^6)
but this explicitly violates the rules of mathematical
precedence, where negation has the same level of
precedence as subtraction.
A critical flaw for any mathematical purist.
Utter nonsense! That is like complaining that German grammar
"violates" the rules of English grammar.
Mathematics is a language. Excel is another language.
If Excel positioned itself as a computer language for expressing
mathematical formulas (cf. FORTRAN), you might have a valid argument.
But if you know the history of Excel (hint: see Visicalc), you would
know that is not the case.
In any case, "when in Rome, learn to speak Italian".