My experience is my own and not anyone else's. I know that it's an older device and can't compare with the newer ones, and that too is a little weird when you've used iPhone for a few years. Even if Samsung phones was so inconsistent, people still said it was the best phone ever made (Note 3). It was far from it.
Like I said, inconsistent battery life and a phone that slows down with time is still the norm with Samsung phones. Nothing you say will change that because you seem biased, as every phone has bugs but some are clearly bigger than others.
FYI my 6S+ is quite ancient by today's standards as well, but it works like a new phone. Same can be said about my iPhone 5 and 3GS when they had their one year anniversary. The consistency is in my personal experience far better.