A founding CTO is more effective than a hired CTO, because the founding CTO has more moral authority to create a consistent system. In other companies there's infighting between people (senior engineers, senior managers) with different architectural preferences (e.g. microservices vs monoliths, Java vs Python). These senior people get half what they want, meaning half your system works one way and half the other. A CTO can hold to their singular vision.

It could be that the moral authority stems from having as much of a full picture as a single person can have over the entire lifecycle of the company, but I think a lot is also just the effect of "I got you here."

I'm glad pg named this effect, since I've talked about the related phenomenon for CTOs with many people.