I'm well aware of the many times that both Microsoft Security Essentials and Windows Defender have been "dissed." Even without questioning the motivations you note yourself that they are "tolerable."
I'm quite tired of the perpetuation of the myth, and it is a myth, that "the best antivirus software" is what, ultimately, keeps you safe from infection. People who browse and download carelessly virtually always get infections. I have to clean them up as part of my living, so I see this up close and personal all the time and a great many of those people have "the best" antivirus and/or security suite programs. Your best offense against infection is an excellent defense, which means paying attention to where you're traveling in cyberspace and/or what you're downloading. If whatever program you're using as antivirus doesn't do realtime scanning, particularly of e-mail messages if you're using an e-mail client program, before you can even touch them then you need to be using one that does (and that's the generic "you," not you, personally).
If accessibility is a concern there are few antivirus programs that are as accessible in all respects as those that come built-in to Windows. Having the ability to control what you need to control is a lot bigger on the practical needs list than what is "the best" in some bench tester's opinion if you ask me.
I worry a lot. . . I worry that no matter how cynical you become it's never enough to keep up.
~ Trudy, in Jane Wagner's "Search for Signs of Intelligent Life in the Universe"