most bots running viruses,you can check this on your task manager when runninga bot with disabled defence so you're right,as for w10 defender is good enought,but sometimes it breaks your nerves blocking almost ebery single thing you run,but sometimes there are files that contain virus running without even taking notice of it,especially if you use or open unknown published .exe files etc.And sometimes it also blocks clean l2 files without reason and let bot virus run in background,at least it did to me when me had w10,still in my opinion you need a paid premium defender that will have completely clean your pc