I heard that myself a couple years ago and was equally disappointed/disbelieving. I started looking for more natural plant-based alternatives, but they're actually a plastic polymer too. If you're out hiking and forage for spruce/pine resin directly from the source: it's still plastic. Very surprising, not what I would have intuited.
It's not my field so I don't know if the plant-based stuff is the same level of harm as petroleum-based plastic, but I would imagine either way it's breaking down into undigestible particles that you're stuck with for life.
As far as an alternative goes for minty breath: nothing stops you from cutting out the middleman and chewing on mint leaves directly. They grow like weeds so if you get some in your garden you'll never run out. I guess the freshness probably doesn't last as long that way, but it makes up for itself in intensity which is just as important for a palate cleanser imo. You could probably get more mileage out of it by turning it into iced tea, then you can sip it whenever you need some freshness.