As vehemently anti-Microsoft as I am (and seeing this with Apple tinted glasses), I have to agree. I believe Apple having full control over their kernel is best for users because of the same arguments you’ve made — I can’t argue that Apple should while saying Microsoft should not.
I don’t really know anything about Defender but I do believe the software vendor itself should be and is responsible. I’m very liberal and I love what the EU is doing in some areas but I think some of it (like this) is a bit over the top.