You did get it right. The PS4 pro did fail. If it didn't fail, Sony would have gave out sales numbers abundantly. Xbox did a similar thing in late 2014 (not that Xbox One was failing, but they were and still are getting obliterated by Sony, and sales numbers would make them look bad).
People asking for proof of Pro's failure should think why Sony isn't talking about it too much.
I think you should should take your own advice here.
What conclusions did you reach other than "must have failed"? Because it looks like you didn't think any further than that.
What other reasons do companies have for not divulging sales figures for every model and revision, even when they meet sales expectations? Especially when it comes to models aimed at a smaller demographic? I'll give you a hint. Splitting sales figures.
“PS4 Pro is running as we had expected, as we assumed, but Pro maybe is doing more than we anticipated,” Yoshida told investors (via DualShockers).
Apple tells us exactly how many iPhone 6S units they've sold, but they're not telling us exactly how much the Plus model specifically sold. That must mean that Iphone 6S Plus failed, right?
No, they brought back the Plus model again for iPhone 7.
Let's say Sony expected Pro to sell 10-15% of what the standard PS4 sells, and as they said in an interview the main target demographic was gamers who mid gen feel that console graphics are outdated and move to PC. And let's say Pro meets this sales expectation and seems to have the effect on the target demographic they hoped for.
Do you think Sony have more to gain or lose from announcing that Pro sold for example 1,3 million units so far? If you look around the internet, and even this thread, people's expectations of what the Pro needs to sell in order to be a success can vary greatly.