That’s overestimating the number of users who are planning to jump ship for sure. We are the noisy ones because we have a lot to complain about right now. It probably more like 1-5% that are planning to leave Reddit indefinitely.
The key word though is “planning”. Because that 1-5% contains an outsized portion of the biggest moderators, content creators, and active users. After we jump ship, Reddit is going to have more spam and abuse (and learn the value of the free moderation they’ve been getting up til now), and less valuable content once you get through that. So Reddit might end up losing half its users as it becomes more useless, even if it’s only a small fraction that’s planning to leave right now.
Not only are YTA, but this will not help you make more money. What would have helped you make more money would be to charge a reasonable rate for API usage. But now you have alienated the users which contributed the most to your success.