Did he??? The light weight gear has been around long before Ray Jardine book ever came out. Grandma Gatewood, John Muir and many others all did it long before Jardine ever came out with his book. To say he made it more accessible I would doubt. The gear to travel ultra-light has been around ever sense I can remember – years before Jardine book.
As for you saying he, “popularized the concept” I don’t know about that. How many light weight websites or videos, books are out there about lightweight backpacking by folks other than Jardine? I think it is safe to say many. This website, to it credit, has a given many, many, many hikers more advise on backpacking than Jardine has ever. To give Jardine or any one person credit either way I don’t believe.
Even if Jardine never wrote his book or step foot on the trail, gear would still have gotten lighter and hikers would still be carrying what they are today.
Wolf