Podman does not require systemd (thank God). I use a simple podman compose up/down in a user systemd file to automatically bring my containers up at boot, but other mechanisms are possible, like quadlets and init scripts.
I use podman regularly, and despite it being a good drop-in replacement like 95% of the time, the 5% of the time where it isn't seamless are super painful. For example, skaffold (https://skaffold.dev/) pukes all over itself when you try to run podman as a drop in replacement. I'm sure there are plenty of other examples, but that one stops me from using podman at work in addition to in my personal projects.
I mean, really, if we keep in mind that formally these are 2 totally unrelated projects, it's hard to complain. Yes, it's almost seamless. But since when installing Podman everyone thinks roughly "I am installing a newer better Docker version", and we all already have a few dozens of custom Docker containers running, it's hard no to wish it was even more seamless and backwards-compatible. I remember the transition process wasn't nearly as smooth as I hoped, and every small glitch is kinda stressful, because you know that currently all of it "somehow works", and if something breaks you probably won't even notice right away.