Can you believe a new iPhone 5 only included a 5W USB-A power adapter?!
Compare that with an iPhone 10 5 years later, which came with a beefy 5W USB-A power adapter.
Compare that with an iPhone 10 5 years later, which came with a beefy 5W USB-A power adapter.
Most people change phones every 3-4 years due to many reasons, physical attrition of hardware being one of it, battery being another, overall hardware not being good enough (speed, capacity) being another.
Almost nobody cares if they can save 5% of battery over that time by charging slowly. Heck, I know I don't. It would be a different proposition if one would lose say 50% of capacity, but even folks in this thread confirm that's not the case for same hardware.
The idea is to have fast charging for emergencies and slow charging for regular overnight charging.
And the thing you plug into the wall isn't actually a charger, it is a power supply. The real charger is in the phone, and that's the one that decides if it needs fast or slow charging, taking into account what the power supply can deliver.