Sorry, this is most likely not true and an unbased claim.
>this is precisely what you would expect in a niche technology as it becomes mainstream: the costs drop dramatically as you climb down the learning curve. one mechanism in that process is that the less efficient producers are driven out of the market because they can only sell at a loss
Yes, this is a common relationship in manufacturing known as wright's law. https://en.wikipedia.org/wiki/Wright%27s_Law
The cost/prices trends for PV are well documented, e.g. see slide 50 here: https://www.ise.fraunhofer.de/content/dam/ise/de/documents/p...
There was no recent transition into "mainstream". The scaling has been taking place for decades already and nothign was "held steady" for 12 years.
If you look at price development during the last months (https://www.pvxchange.com/Price-Index) you will notice that the prices drastically dropped by more than 50% during the last year. This is a clear sign of oversupply, regardless of discussions regarding tariffs etc.
To explain this kind of price drop based on the history scaling laws (24.4% per doubling) would require the total production capacity (and installation) to have more than quadrupled over the last year.