Decision is kinda easy - pro series battery was always mediocre.
From there it either works for your use case or not. Like i have 15 pro, had 14pm and 15pm. Wife has 16pm.
The reality is that pro max is totally in different realm phone series. 14pm hand me down with shot battery still worked 8-10 hrs. My new 15 pro works on average 7 hrs but on 4g internet and 5.5hrs with bad 5g reception. At most I squeezed out couple times 11hrs by listening to headphones (music cover static on screen) or browsing safari on wifi with lower brightness. Basically you have to dance around it a lot to get more than 8 hrs.
My wife’s 15pm and now 16pm just live 13-16 hrs every day no matter what you do. For me that becomes a 2 day phone to be honest, when she hands me down those pro maxes every year.
I kinda enjoy smaller phone but it is not that small and light. If anything ergonomics wise regular 16 followed by plus works better - pro line is just heavy. Pro max albeit heavier has a better wider grip if anything.
My next phone would be pro max. Pro works for my lifestyle (8hr office) where i use my phone 30 min on breaks and mornings, maybe listen to music with screen off, and use heavily in the evening. Sometimes it makes to bed charger sometimes doesn’t last till sleep time. But on outings like exploring major cities, this pro phone is a toast before the day ends so no maps or anything unless hauling powerbanks.
In short, 10 hrs on pro if very lucky cause that is not a regular case. Regular case is more like 7-9hrs.
For pro max, regular is 12-15.5 hrs.