Terence, you state that there are good dancers who compete in pro/am because they cannot find partners.
While you may be correct in some cases, I believe that it is equally true to say that many of them do not want an amateur partner. I am making an observation and not a supposition.
A couple of years ago, I listed myself on a couple of partner-matching boards. Over the intervening months, I received a surprising number of responses (surprising given my age).
Unfortunately, every response - without exception - involved a lady in the same situation: she was competing in pro/am and wanted to practice more but couldn't afford to pay additional lesson fees just to do so with her pro.
I did give one of these women a try for a few months. As it turned out, she kept trying to shift more and more of the cost of our lessons and practices over to me (I described this situation in another post). When she let it slip that she was spending more on her pro, I decided to stop being a chump and dropped her.
I went back to the partner-matching sites and changed my notes to read "no pro/am competitiors." The responses stopped.
jj