I went from 12 Pro Max to 15 Pro Regular. The screen on the Max is bigger, but it feels kind of the same content-wise. It’s the width - even the iPad Mini offers a substantially different experience. On the other hand, Pro Max is more difficult to wield.
The battery life is quite a bit better on the Max, so these days when I’m outside I carry a small Mophie or Apple’s MagSafe Battery pack (since I charge only to 80% and I don’t like to drop below 30%, otherwise I wouldn’t need it).
I’m happy with the regular Pro, and I would be happy with the Max. I had a Max for three years, I’ll probably have this one for three more, and I’ll see what I’ll get after. But for now, it’s great to be able to comfortably use the phone one-handed. And it’s much easier to reach the action button as well.