You can't just wave your hand and say that some lesser known "no names mentioned" product is better than Defender because you want it to be. If you have evidence that some AV product is out-performing Defender, it's extremely selfish and negligent to keep that information to yourself.

I'd much rather trust MS with Defender over some lesser known AV product which likely doesn't have billions of dollars, unfathomably large samples/datasets, and extensive experience with APT's.

As pointed out, no one really has a better incentive to detect and eliminate virus's than MS does in an effort to make their OS virus free.