in 2007 i was riding a DH bike with a 12.5" bb height and something like a 64° HA.Nah. I understand exactly what you're saying, just from a different perspective.
You are now focusing on one particular aspect of MTB design/devo. That being geo.
The fact that it has developed from road bike geo should be no surprise.
The fact that almost everything had to be developed from road bike stuff should be no surprise.
The fact that change takes time should be no surprise.
Back into the waybackmachine, to 2007. Developing the "magic link bike". LOTS of input into what that bike should be. in a category that really had no category, enduro hadn't been invented. It was tough to sell slacker than 69 Degree HTA. Not becausae of market demand. Because this is what the hard core, north shore riders of the time were used to. This wasn't dentists. These guys could ride.
But they were afraid they couldn't sell different geometry. Ironically, while investing in a geo changeling suspension