For linking an acoustId, I agree. A CD or other original digital source is really the only reliable source for an acoustId. Analog sources aren't trustworthy, and I avoid submitting acoustIds from an analog source eg. from digitizing an LP. I do make an exception for albums I have that are rare and out of print, where often an original digital source is simply unavailable. Picard usually does find matches for my less obscure digitalized vinyl tracks, so I am fairly confident that my equipment is functioning well enough for this to be useful.
Regarding unlinking sources based on "statistics", it seems the best way to clean up some of the out of control acoustIds on popular tracks. Pick any popular tracxk, eg. Eagles Hotel California and you're bound to find dozens of acoustIds. Since an acoustId should be unique for given audio, this shouldn't happen, but it does. In my experience the vast majority of those acoustIds have only a single source, and only one will have a significant number of sources. For this recording, it appears to be 8815564 that sourced our track 1305 times. What are we to make of the track by The Beagles (a UK tribute band), sourced 5 times? If it's also valid, then we cannot rely on acoustId to identify unique audio at all. I say unlink that one; it can't also be right.
Some due diligence is required, of course. For example, here is an acoustId for Make It With You by Bread. Again, a very popular track, dozens of acoustIds on the main recording. The acoustId also shows a link to a recording by David Gates. Seems like a similar situation, until you discover that David Gates was the singer for Bread, and the track is from David Gates Songbook. So, it could be a later solo recording, but it could also be the same Bread track, misattributed to David Gates instead of his former group. Best left alone, I think, until some more research or a sound check can be done.
I'd like to understand better why errors like this are so common. There seems to be some serious issues in the process by which editors are attaching acoustIds to recordings.