I hate it when I see people complain about the batteries being smaller. If Apple can throw R&D money at getting the same battery life with smaller batteries they should. Having a smaller battery means smaller charge times, but also means you’ll charge it less which has a massive affect on the environment and energy usage over millions of iPhone users.
That is incorrect. Better phone efficiency makes a difference, smaller batteries do not*
Obligatory water analogy.
Say you need 10l of water per day and you have a 100ml iPhone 7 cup and a 90ml iPhone 8 cup, then you either need to refill the 100ml cup 10/0.1 = 100 times (iphone 7) or 10/0.09 = 111 times (iPhone 8). It's still the same total amount of water (energy).
Oh, and assuming a daily charge capacity difference of 200mAh * 365days per year = 0.073kWh/year (== powering a lightbulb for 1 hour / year). Not including charger inefficiency (say 15%), but as I explained above the issue you have described makes no sense anyway.
*The only environmental effect that that is correlated with less capacity, assuming the same battery technology is less capacity -> less materials (-> cost saving, which is why Apple does it)