[Yo-Yo]

Faster charging lowers battery life. Since iPhones cannot easily change batteries, they are designed to charge slower.

[conservatism_IS_compassion]

Battery capacity matters as well. My phone has a 3,400 mAh battery and it takes longer to charge than, for example, a 2,000 mAh battery, but it also lasts a lot longer. - Rodney Dangerfield

I use my iPad charger, which at 2.1 amps, recharges my iPhone 6 faster than the fastest time listed. . . But Apple doesn't include one with the iPhone. - Swordmaker

Faster charging lowers battery life. Since iPhones cannot easily change batteries, they are designed to charge slower. - Yo-Yo

IMHO these three comments pretty much cover the waterfront. Swordmaker's iPhone very well might give a shorter lifetime because of the use of a higher capacity charger.

I confess to an incomplete understanding as to how a higher capacity charger can work without imposing a higher voltage on the battery. I would assume that it has lower internal resistance, but that would only say that the the voltage doesn’t drop as much from its nominal value under load.