I am not sure what to do about the burnout problem. The way he described it is very on point though. Since everyone working on the project is overloaded there is a great feeling of things only get done if you do them.
Most of my open source work was in the pre-GitHub days when we used mailing lists, not pull requests, to build community. I do think there was something better about that for the project itself as it encouraged a lot more discussion and community building. PR's and Issues become silos and are not great for general discussion. I think they also encourage drive-by contributions which honestly are intoxicating initially but once you see people are not coming back become defeating.