Not only would it be an arbitrary departure from the original canon

I don't think it would depart from canon, and it would be very much in line with fanon: the fanfiction involving Dumbledore shows him as someone who thinks he knows better - and has no qualms about misleading or mistreating anyone to get them to do as he wishes. Canon never states this outright, but it does give you all the evidence you need to make a decision: Dumbledore, with full knowledge of the situation, condemned Harry to spend nine years of child abuse under the Dursleys.