I thought Google recently announced changes to this requiring a developer account to side load.
Hopefully, they'll see just how ineffective their measures are, and abandon before applying the plans to the rest of the world.
Why do we consider user installation of software abuse? Plenty of people install software from non-play repositories simply to prevent Google from getting data about their app profile.
I disagree that such protections (at the expense of the power users) are necessary, but, OTOH, you cannot just ignore such issue existing in the first place, because it does exist, and Google already does have the tools to combat it (by scanning all apps regardless of origin, and blocking malicious ones).