I don't have figures for modern yields. I hope the yield is better. But I think there are fundamental difficulties with matching up the sapphire and silicon crystals that tends to produce faults.

I'm astounded HP made commercial products out of a process with such a low yield, I dont know how that was economical. (though none of the HP gear was exactly low margin)

The HP Journal article mentions the 9% yield as if they are perfectly fine with it. They were building these chips internally for high-margin gear (as you said), so it probably didn't matter if the chip cost $10 or $100, as long as it has the performance that they need. It's a completely different market from microprocessors such as the 6502 or the 8086, where customers are looking closely at the cost of the chip.

and RF components are still in that space to a greater or lesser extent too.