The biggest price increase didn’t even come from tandem OLED. The largest increase was back in 2018 when Apple simply began positioning iPad Pro as another type of computer. The product steadily bumped in price from $749, $799, $999, $1,099, to $1,299.
I think that you are seriously underestimating the cost of the processor and screen in the current design. The price has gone up over the years, yes. But the technology has advanced FAR beyond the rate at which the other iPads have.
If you're wanting to cry about the price of the iPad Pro - how about you have a look at the price of the iPhone Pro - which has massively inferior processor, less RAM, inferior screen, much smaller screen, smaller battery, no stylus support, etc.