grimmgoose
Adventurer
The Keeper Rulebook is the core rulebook. Yes, there is an investigator's guide, but it's basically the inverse of how D&D does it. So I mean, I guess that makes you technically correct, but when people ask, "how do I play CoC?" the answer isn't, "well first, buy the Keeper's Guide and then the Investigator's Guide..." it's: "buy the Keeper's Guide. If your players want something, use the Investigator's Guide" (which is basically a copy of the rules from the Keeper's Guide, along with some 1920s setting information).Pathfinder and Tales of the Valiant would like to disagree on this. And sure, you can say because it's Paizo, a direct WotC competitor, but Call of Cthulhu has the Keeper Rulebook, which is their DMG. Drakkenheim series also follow this, and they're 5E (two books with a MM on the way).
The rest of what you mentioned are all d20 games, which are heavily influenced by D&D. I also didn't say D&D was the sole TTRPG that did it, but that
Requiring a separate purchase for GM advice is exceedingly rare.