That's not true at all. I worked for 3 years on a non-profit that funded itself and it received external donations and investments. This is not "either self-funding or external-funding". The whole idea of a nonprofit is that instead of sharing the surplus of revenues between shareholders, leaders or members, it will invest the surplus further into the company development and projects. It has nothing to do with scalability.
Having managed a non-profit and having worked at a very successful one before, this just makes you sound so out-of-touch it's not even funny.
Yes, some non-profits are driven by donations, but many are not.
> So it's far better for a for-profit to solve a given problem than a non-profit, as they are inherently more scalable.
If by, "more scalable," you mean, "less accountable," then you're correct.