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.
I realize I am in minority, but for me, if project uses a mailing list I am more likely to do a drive-by contribution (compared to no contribution at all). Just doing git send-email is much easier compared to figuring out how to create whatever pull request is called in whatever forge the specific project is using.
Which, for drive-by contributions, does not really matter. It is a problem for long term contributions and project managements in general, true, but there often is some tracking system present (patchwork, debbugs, ...).