The process to produce industrial diamonds (essentially, very hard dust) does not meaningfully help scale the process to produce first-quality synthetic diamond gems for jewelry.

As your quote points out, synthetic industrial diamonds have been available for many decades. But it is only recently that synthetic diamond gems have achieved popularity and price advantage for jewelry.

Diamond dust used to be the main industrial product. But as diamond synthesis has improved, cutting tools are now using larger diamonds.[1] This has been a big win for the well-drilling industry. Newer bits cut rock, and with diamond, they last long enough to get the job done. The classic Hughes tricone bit, the thing that looks like a set of bevel gears, is not a cutter. It's a rock crusher.[2] It cracks by compressive force.

(Patents were really strong back then. Howard Hughes, Sr. became the richest man in the world by buying the patent for the drill bit. He then manufactured bits and rented them out for a fraction of the profits from the oil well.)

[1] https://www.slb.com/products-and-services/innovating-in-oil-...

[2] https://www.texasmonthly.com/being-texan/texas-primer-the-hu...