The idea is that in five years time you have say 80% of the original battery capacity and performance.
So that’s 80% after spending five years charging rapidly now and then when needed at 120W
80% after spending five years charging very slowly at 20W the end of every day.
The point is they are both designed and engineered have the same lifetime regardless of how they are charged.
If you put out a phone which nuked the performance of it after one or two years of charging at 120W then yes that would be pointless and damage reputation.
That’s what engineering is all about. 20W isn’t the optimal speed that should be the max until the end of time. It’s basically what was possible back in 2018. It’s just Apple being lazy and knowing it’s followers are loyal and complacent. iPhone 14 will have 40W and they’ll go look we doubled it aren’t we clever.
And all batteries have built in thermal management so even the 20W will be its peak in the same way 120W will be its peak on that battery. No battery to my knowledge would run at the max potential from zero to full.
It’s the same principle with EVs in getting away from the ritual of plugging in every night and slowly charging, to being able to top up when needed rapidly at a fueling station (like petrol/diesel now)
5000 mAh and 120W seems a decent mix without adding too much extra weight. Apple will now doubt have this in its labs right now for future release. It probably could have released it now if it that was the marketing plan.
How the 13 pro max is 240g are they making it out of lead. There’s no excuse if it turns out it has 4000 mAh