If you watch the video you find that he has valid complaints, and he's not opposed to paying Reddit but thinks these terms are designed to sink 3rd party apps. Some highlighted points.
* The API access charges about 10x the price compared to the revenue per user they would expect if the users accessed reddit via web or official app.
* There was 30 days notice of the new pricing. He has many customers that pay per-year that he is going to lose money on until renewal.
* The price is too high. Compared to similar platforms that charge for API they are charging way more.
* An individual from the company called him out for having 'inefficient' code, which he took personally and mounted a good defense of his usage.
* The API is losing feature parity with the first party website/app.
* Reddit is itself building a bigger business on the backs of reddit users generating content. Many of those users use a 3rd party app. In fact, 3rd party apps were largely responsible for transitioning reddit into mobile usage. They seem to be overstepping their position in the ecosystem.