I've had friends that have been fire fighters and I think the burnout is real. They're not dealing with structure fires much anymore which is what a lot of their training deals with. Rather they do a lot of social work in the area taking care of the unhoused, disinfranchised, mentally disabled, etc... all while having this unique training.
And this is also describing fire fighting in cities. In smaller town and more rural areas the workload is different. Not so much mental health, a lot more of the workload is accidents, but where it can really change is rural land fires in droughts. Get a dry windy summer and you can end up working for months at a time.