I really like this. It has a similar (but different) feel than the answer involving Poison Ivy and Mr Freeze (which at the end I was abstracting as "believable experiments gone wrong with unexpected but somehow credible outcomes").
In the case of para humans you're saying, powers are well constructed within the limits of the world they live in and are related to something traumatic (and not necessarily reversible) which gives them abilities related to the event.
I admit ignorance in their respect and will look more into it. Thanks!
That's right! In a sense, Batman is very grounded as a comic book in that several of the main characters (Batman and the Robins) all are well trained people but with no super powers, so they are believable!
There is another answer below about Poison Ivy and Mr Freeze which I also liked and commented on and which (coupled with your answer) points to how much of the lore around Batman is well constructed (that is, characters and villains have a "believable" and well thought origin story)