His insight was that the model was repeatable and scalable. The assembly line kitchen they developed not only made making burgers fast but also made them incredibly consistent. Because of this he could franchise the restaurants and be assured that quality would be consistent among them despite being operated by different people. He never intended to open large numbers of his own restaurants - just enough for experimentation purposes.
To this day this is a major selling point. When travelling you can take your chances on a local place or go with what you know.
No. Most startups are designed to grow fast. But many non-startups are designed to grow fast. There is overlap in the Venn diagram, but they are not the same thing.
> If Ray's original plan
If that was Kroc's plan, you'd be right. Do you have some evidence it was?
As far as I can tell, he spotted an existing restaurant that had already found product-market fit and just scaled the operation using variants on known franchising approaches. I also haven't seen any evidence that at the time he foresaw suburbanization, white flight, and the resulting increase in value of heavy branding, trends that were nascent at the time he joined McDonalds.
I'd say it was more akin to the top-growing restaurants of today, ones I point out elsewhere in this discussion. They are fast growers, but they are scaling mild variations on well-known business models.