i would disagree about this - i know of several prosthodontists doing very well. one of them is known for the best removeable pros in town, and he charges a lot! like $3K/set of dentures
the other is in a group practice w/a GP and a periodontist, the three of them are known as a one stop shop for great implants
another one i know has a very successful esthetics practice
you make your own opportunities, if you love pros do it!