Those aren't lonely, quirky, painful endeavors.
And while I have no doubt that a "popular" author's fans
would follow them to another publisher. There can't be THAT much evidence to support such a theory. Namely because anyone signing a contract with a Big 5 publisher isn't likely to be going anywhere else very soon. Even if they wanted to. There's no willy-nilly Big5 publisher swapping going on ...
especially among authors whose fanbase would be large enough and/or zealous enough to survive such a hop.