I'd say that the statements from the guy's students are pretty damning evidence of what he's been preaching.
It would still be nice to have some other confirmation. Mims only gave his paraphrase of what this guy said. Single-source paraphrases are about as accurat as a single movie review.
After he left he maintained ties with the company (i.e., he wrote tech docs for them).
Of course, Mims left MITS before the Altair was invented; Mims sold his interest for $100.00. Mims should get little credit for Gates use of Basic as Mims wasn't part of the company at that time. pdf link Mims left in 1971, the Altair was introduced in 1975.
As to the legacy leading to Gates, my point was that without Mims, there'd not likely have been a MITS; without MITS, there'd have been no Altair 8800. Without the Altair 8800, Gates would have avoided the college drop-out route and become a successful student. :)
To cut Mims out of that sequence would be like cutting G. Washington out of the history of the USA, asserting that he has no claim to the greatness that the nation manifested over the next couple of hundred years, because, "he was long dead when most of that stuff happened." :)
(I said that he was a "father" of the PC, not the "guardian" -- in the same sense that GW is referred to as the "father of the nation.")
I wonder: If Gates & Allen hadn't been the first ones to develop a programming language for the Altair, would we all have been programming in Pascal (or some kind of Tiny Algol) a lot sooner instead of BASIC, or would CP/M assembler be the top-dog language, or <shudder> FORTH?