If you look at the first binary patch for Equation Editor, it's very well done: https://blog.0patch.com/2017/11/did-microsoft-just-manually-... . The problem was that when they fixed it once, other researchers started fuzzing Equation Editor and found many more bugs. Bringing a C++ program from 2000 up to modern security standards when you don't have the source code isn't really feasible, it would be an endless series of whack-a-mole binary patches. I don't really blame Microsoft for dropping support, especially when there's been a replacement equation editor in Office since 2007.
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If you look at the first binary patch for Equation Editor, it's very well done: https://blog.0patch.com/2017/11/did-microsoft-just-manually-... . The problem was that when they fixed it once, other researchers started fuzzing Equation Editor and found many more bugs. Bringing a C++ program from 2000 up to modern security standards when you don't have the source code isn't really feasible, it would be an endless series of whack-a-mole binary patches. I don't really blame Microsoft for dropping support, especially when there's been a replacement equation editor in Office since 2007.