I feel like the perfect compromise would be to separate the definition and engine/UI components and allow some interoperability between the two. So if I want to

I feel like the perfect compromise would be to separate the definition and engine/UI components and allow some interoperability between the two. So if I want to, I can use Kaspersky/McAfee's definitions (probably on some kind of paid subscription), but the engine/UI is Defender, so no bloatware or nag screens. Conversely, if I want to, I can install Kaspersky for whatever extra bits they do, but still fetch the latest definitions from Microsoft.