Interesting I get downvoted for something which just happens to me and I can prove if you sit next to me. It's slower, much slower. With any charger including the original one which came with the phone. I create apps and have a ton of devices; it's not like i'm an Apple fanboy or whatever, it's just an observation.

I didn't comment on battery life because it is almost impossible to measure since it depends on many factors. Charging time on the other hand is easy to measure. The Galaxy S5 charges very quickly compared to other phones. I'm not suggesting that you are lying but that your charger probably didn't let the phone charge as fast as it can.

I do not know the reason but I would love to know it; I use the 5s + s5 together every day, all day for business. And it is very simple; after about 5 hours the one I used most will be dead (it differs per day which one that is) and for the s5 the day will be over; it will take more too long to charge to even put in the loader, while if it's the 5s, it'll be fully in a jiffy. Now I could have a faulty model (I can rule out chargers as I have many of them, always use wall chargers and official cables) but I have the same experience with every other non-Apple phone I have. For tablets I have; iPads + Windows 8 tablets take the longest to charge, Android the shortest.

Anyway; it does not really matter; I like Android phones but for me short battery life (like you said, depends on many factors and is about similar on iPhones) life is killer and then long charging adds insult to injury.

It should depend (mostly) on the charger and battery size.

Try to charge the S5 with the same charger you use for the iPhone and my guess is that they will take more or less the same time.

Never use third party chargers of dubious origin, apart from being not safe they tend to be slow.

I do use the same charger.