It's not clear to me how much experience with serverless architectures the author of the parent comment has, but speaking as someone with plenty, the operational costs of serverless are at least equal to managing stateful infrastructure, with much less control when things go wrong. Lambda was a major step up in long term predictability compared to for example App Engine, where there have been plenty of instances of overnight unannounced changes, or changes announced with incredibly short notice period, requiring developer time rather than ops time to bring an application back to service.

On the ops side even with a platform like Lambda, training an operations team to take over maintenance of a nested spaghetti of random interlinked services and bits of YAML trapped in random parts of the cloud is a total nightmare. The amount of documentation required and even the simple overhead of enumerating every dependency is a long term management burden in its own right. "The app is down" -> escalate to the developers every single time.

Compare that to "the app is down", "this app has basically no ops documentation", "try rebooting the instances", "ah wonderful, it came back"

I'm pro-cloud in many ways and even pro-serverless for certain problems, but let's not close our eyes and pretend dumping everything into these services is anything like a universal win.