Yes, Gary was there. Yes, Gary was the owner of TSR.
An owner. A large but not majority (for most of his time with the company) shareholder. The Blumes controlled more shares for almost all of TSR's existence pre-Williams takeover. Gary exercised an option at one point to get majority ownership, but Brian had the right to exercise the same kind of option and take that majority away at any time, as he finally did when he reached agreement with Lorraine, after Gary first promised to buy out the Blumes and then strung them along and didn't follow through.
Gygax didn’t just use ideas that were in the zeitgeist, though. Tons of 1e stuff was originally created for 0e, or contributed through letters, magazines, etc. and then rewritten by Gygax for 1e. Meaning specific rules, spells, monsters, even character classes.
One of the primary purposes of 1e, after all, was to get out of paying royalties to Arneson. That went to court, and a judge ruled against Gygax. From a legal perspective, 1e is not his sole work. And that’s setting aside all the other contributors.
Nobody is disputing that those are mostly Gygax’s words on the page. But rewriting something does not make it your creation.
Right. He composed most of the text of the core AD&D books, and that plus him putting his own name on the cover solo to claim all authorial credit is why we all recognize his distinctive voice. But he did not write and design
all of it.
The
Greyhawk supplement for OD&D, for example, from which we get a ton of the changes which would become codified into AD&D (variable weapon damage, non-D6 hit dice for PCs, most benefits from ability scores, a ton of core spells, the multiclassing system, new monsters) was co-credited to Rob Kuntz. I don't think I've seen anyone create a clear breakdown of who wrote what parts, but even just going by cover credit that's a significant chunk of AD&D which Rob apparently contributed to. Same with the concepts in the
Blackmoor supplement, whence originate Monks and Assassins, and a bunch of the aquatic monsters in AD&D. Officially the book is credited to Dave Arneson, although apparently Tim Kask (credited as editor*) basically wrote it, working from a basket of rough notes by Dave, and with some input from Rob Kuntz and Steve Marsh (who are both thanked at the front of the book for "suggestions and ideas").
The Ranger was created by
Joe Fischer in its original form in The Strategic Review, and Gary expanded and modified it a little for the PH. The Thief was created by
D. Daniel Wagner from the Aero Hobbies crew in Los Angeles, and sent to TSR by Gary Switzer, a member of that group. Gary modified and expanded those rules for the OD&D and later AD&D versions. To my recollection Gary later indicated that some parts of the rules he had only a partial hand in (like the unarmed combat ones, IIRC?), but I'm not finding an immediate text reference. I think there's more explicit confirmation in
PatW or
Game Wizards, but I'd have to go look for quotes.
So yeah, while Gary indisputably was the primary author of OD&D and AD&D (based in large part on concepts from Dave's Blackmoor game), one thing we've learned since the histories started being researched is that a bunch of people actively contributed to designing the content of those books. Dave, Rob Kuntz, Tim Kask, Mike Carr, Steve Marsh, Joe Fischer, and D. Wagner all included.
*(An interesting presage of how Holmes would be credited as editor on the first Basic set, though he wrote it based on the rules in OD&D, and similar with B/X for Moldvay, Cook, and Marsh, and BECMI for Frank Mentzer).