First, if you are comparing the battery life of the zmax pro on marshmallow to the battery life of the first zmax running stock KitKat then of course the first zmax is going to win that contest because you are talking about two completely different versions of android with major differences.
However, if you compare the battery life to what the original zmax got after installing lollipop or marshmallow you'd probably find that it's the same or maybe even better.
When you take into account the fact that the zmax pro has a bigger display with a higher resolution, a faster processor, and a newer version of android, you can't expect it to get the same amount of battery life as it's predecessor. With all these differences taken into account, zte would have to put a much larger battery into the phone for it to get the same battery life as a lower spec device (the original zmax) running an older version of android. This doesn't seem very practical to me since the zmax pro already borders on being impossible to use with one hand even for someone like me with fairly large hands.
About the battery stopping charging before it hits 100%, you say some others (me) are trying to "paint" this as a "feature" rather than an issue but I was only suggesting a possible explanation. I wasn't trying to "paint" anything to be something it isn't. I was making an educated guess based on the fact that the only time this ever happens on my phone is when I'm playing need for speed (which really gives the phone a workout) when the battery and CPU are already getting hot. You say it is definitely a defect and are presenting this as irrefutable fact so where is your proof that the developers didn't implement it as a safeguard to keep the battery and CPU from overheating (which happened all the time on the original zmax)?