You are probably right for something like a Pihole, which can easily run on a RPi 3 as well (I think I'm running it on a 3... maybe even a 2.) My fear is something like Jellyfin (which it is not suited for anyway, I know), combined with the fact that my stack of Pis is in my meter cabinet, so a fairly confined space with very little air movement, also passive. Running Jellyfin without transcoding has my Pi 5 running at just under 50 °C.