Your research is out of date. Avast has proven to be over 90 percent effective at finding malware. As with all computer OS's it depends on who gets the malware first typically.
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As with all aspects of security time is of the essence. Out of date info is dangerous. This test was done a few months ago and completely contradicts their results from the previous year. The times are changing.
AV-Test Revises Android Antivirus Results
It's also important to note that within the last six months things have changed drastically in the Android market. Malware is out there and often slips past Google and gets into the official store.
As a security expert I'd expect you to know that all forms of software are vulnerable to exploits. Security isn't a one stop solution. It's a layered strategy that works. Google is layer one (or Amazon if you prefer), you are layer two by being careful and reading the fine print, and AV is layer three.