I'm finding the "positive sum" language around coins really misleading.

It's literally the opposite. If the way users make money from their content is when other users buy it, it's literally zero sum, financially. Not everyone can be making money, unless external capital is being injected from a another source (which is losing money).

Yes, unless they represent value being generated outside of the coin itself. Many app tokens creating products or service of value can genuinely represent real external value that can grow over time in a non-ponzi way. The governance tokens of DeFi protocols that provide real financial services are just one example.