I went down the same route this year, having had pro max's every year previously, though I did try downsizing back on the 13 pro and ended up swapping back to a max a few days later, the battery drained far too quickly and I hated the screen size.
So this year I was very sceptical about down sizing again, but its been nearly a week now and I'm more than happy with the size, that small increase though minor and maybe the lack of the notch has helped.
The battery isnt quite as good as the Pro Max but so far it isn't far off in my usage case and I will easily get more than a day out of it.
It comes off charge at 630am and by the end of my working day at 5pm on the 15PM I would have gone home with about 80-85% battery, with the 16P I have around 70-80%. I take a few phone calls, send a few messages, play a game for 30mins some days, and maybe watch a couple of youtube videos.
I've noticed that I have an update finishing in the background again this morning, so theres a chance it could improve more when that finishes, plus dev's will surely update apps to optimise which will also help.
Time will tell, but so far i'm more than happy with it and glad I made the switch this year.