Scott Lobdell, for example, was writing for three books: Red Hood, Teen Titans, and Superman. They sell in basically that order. Lobdell recently left Red Hood in order to put more of his attention on the inferior performing Superman book, while James Tynion IV was brought on for Red Hood (a writer who has almost no experience, and currently is helming the commercial flop of Talon).
Just look at it objectively. Lobdell was writing both. Hood performed better than Superman. This means the Lobdell writes Hood better than he writes Superman. Taking him off of what he's doing best, and putting him onto what he's doing poorly at, will not make Superman into a top end title. But handing Red Hood off to a new writer certainly does have the potential to hurt that book.
I just wanted to point out that your numbers are off.Red Hood has been outselling Superman for the last two months... because it tied in to Death of the Family. In November, it was selling 37,000 copies, up from 35,000 the month before. Superman, on the other hand, has never fallen below 50,000 copies (which might change with the February numbers, but still. You are right that Teen Titans has been in the middle... outselling Red Hood every single month, often by as much as 8-10,000 copies. And the 'commercial flop' Talon has fallen to 31,000 copies, not that much below Red Hood's lowest numbers, and did not receive a boost through an event. This does not support "Batman family rules all!", it supports an event tie-in with DC's most popular book will boost sales significantly (see also: Court of Owls).
DC is not going to cancel Superman or Action Comics because of what those titles represent (unless their numbers really start to tank and consistently sell below 15,000 - which is not going to happen). On the other hand, putting their hottest writer on their most iconic character (yes, more iconic than Batman) will probably lead to a significant uptick in sales.