Yeah uhhh...there is a problem with your rant and its the simple fact that Windows Defender doesn't work worth a shit at least not in the real world with real bugs.
Allow me to introduce myself...Hi! I'm the resident PC shop guy, its my job to clean up the messes that Joe and Sally Average get themselves into. I'm popular enough I don't advertise anymore and just get customers by word of mouth so I must be doing something right and Windows Defender? Yeah its a POS. I've had customers come to me with just about every free and paid AV there is out there and WD? Those PCs are always the worst infected by a country mile. Sure it uses less resources, I'd argue because it doesn't do much of anything it really doesn't need lots of resources in the first place. Sure its better than nothing but that ain't saying much.
From what I've seen at the shop? The best paid are Eset and Bitdefender, the best free are Avast, Comodo, and Adaware. With those AVs you hardly find anything and what you do find is usually pretty benign stuff like PUPs whereas with WD? Those are the ones I see the "This PC is locked by the FBI" bug, the Security Tool 201x bug, all the real nasty shit just seems to blow right through it. Makes me think its like Norton was back in the day, remember that? In case you don't back when Norton was hot shit all the bug writers tested against Norton because they knew it was included by default with a lot of OEMs so if your bug could bypass Norton? That opened up a LOT of systems you could infect. I bet the same is true for WD, bug writers test against WD because they know its the default on Win 10 and lazy users won't change defaults so there ya go, lots of targets.
So I really wouldn't use WD or MSE on anything that you actually worried about getting infected. Sure it has its uses, I have it on my gamer rig but that is really nothing more than a box that plays Steam games so its really there just for peace of mind more than anything, the quad beside it I actually use for surfing? That has Comodo IS on it.