As a matter of fact my current perpetual gmt is the best timekeeper I ever owned. That being said I had a similar experience with a watch from different brand: it was a terrible timekeeper and the customer service couldn't find anything wrong with it. As you, I ended up selling it.
Beyer was one of the first Swiss Ulysse Nardin AD after Rolf Schnyder acquired the company. I was privileged to have dinner with both gentlemen about 20 years ago. I last saw Mr Beyer three years ago when I took my younger daughter to Switzerland. He was already frail back then and we visited him at
Cartier AD in Hong Kong sold me one at 30% off in 2003 and to sweeten the deal offered a mechanical Basculante at equivalent of 1600 USD. Tnat was before boutiques became a commonplace. How the times changes. And I still have both.
The power reserve hand on my watch is white and not black as on the picture you posted, so I have no issues seeing it. I agree on GMT and even 24 hours indicators. They are very small and with my aging eyes I can barely see them. The watch is very cool though and is one of my favorite travel compani
The only explanation I could think of, is that they came from different batches and there is differences in either age or manufacturing process. If Blancpain keeps an old stock of spare parts, individual pieces can age at a different rate.