all Bitcoin ASIC companies had to derive their works from existing the current SHA-2 ASICs, starting from scratch would have cost far more than the Bitcoin economy could have supplied, and far more than ASIC companies could afford to spend at their current price points.
That is not correct. Bitcoin ASICs are essentially glorified SHA-2 calculators. Input binary blob & target. Output any nonces which result in SHA-2(SHA-2(blob+nonce)) < target. Not to take anything away from what the Bitcoin ASIC companies did but the chips are just performing the "math" of the SHA-2 algorithm. Most of the "smarts" is not the customs ASICs but in the cheap micrprocessor (Rasberry Pi or embeded computer). Far more complex chips are made in universities every year as academic projects. There was an ASIC in your hand calculator from the 1970s. It didn't cost a billion dollars to design either and the tools were a lot more primitive back then.