I suspect the extra weight may be from the slightly larger size, and also the microfiber lining on the interior, which wasn't there on the 13 Pro case. I just weighed both of mine and got 41g for the 13 Pro and 42g for the 16 Pro. Either way, a 1 or 2g weight change is negligible to me. Maybe even more surprising to me is that they're both heavier than the Speck Presidio 2 Grip (40g). Before weighing them, I would have guessed just from looks that the Speck was significantly heavier than either of them.
The buttons are shifted ever so slightly downward in the 16 Pro case. I've hit the Action Button a couple times by mistake, but it's mostly because I'm not used to having an Action Button at all - my 13 Pro just had the mute switch. I'll have to get used to the fact that the uppermost button isn't the volume up button anymore!
This pic is the 13 Pro Sheath lying atop the 16 Pro model, showing the difference in location (and also the metal vs. TPU buttons):
View attachment 2431569
I'm undecided on whether I like the metal buttons better or not. They operate much more smoothly and are easier to push than the TPU buttons on the 13 Pro, but they're also more prominent from the case and more subject to me accidentally hitting them. No real big deal since it usually just means I bump my volume up or down a notch or accidentally activate the screen, but something I have to get used to.
I'm also not so sure I love the microfiber lining. I usually remove my case every couple weeks or so and give it a good scrub in the sink with a brush and some dish soap, hopefully the microfiber won't retain water and need to dry out before I put the case back on my phone.