Purigen does not remove the ferts that we dose in planted tanks.
The only case here is really financial-related. Plants do what purigen does but perhaps not to the same degree.
People have had success with and without Purigen. There's no other harm to using Purigen other than to your wallet.
I have had the exact same success with the same tank with the same filter with and without Purigen. It's not going to turn around your tank into something different, outside of being cleaner.
On the flipside, I consider Purigen cheap as a little goes a long way, and it basically lasts forever. Outside of the bags it comes in (I used to get it in bags), it lasts forever. I have one pouch that is almost 5 years old and still will be pure white after bleaching. As said, I only run it on nano's now so the pouches aren't excessively expensive, fit in most filters, and go forever.