Yes, it's ironic that

Bigger is not necessarily better, yet nonprofits exist in a society that believes the opposite.

I think you are absolutely right that "the goal cannot be growth." So what we need to do is redefine what the goal actually is. The $50 million or $150 million solutions are not possible, and wouldn't even necessarily be viable or effective (and thus desirable).

So what's a $50K or even the $5K solution look like? It's not about small being better, so much as small being effective.