Then you fall into the second category. Or you're just ignorant.
Well, I'm a copyright lawyer, so I doubt I'm "completely and totally ignorant of the law." Have you considered the possibility that your analysis is wrong?
Since we're talking about works that haven't been around long enough to have their copyrights expire, that's totally irrelevant.
Just thought I'd mention it, since you did make a rather broad statement suggesting that works cannot enter the public domain unless deliberately placed there by the copyright holder. While copyright holders can put works into the public domain, it's not true that that is the only way for works to enter the public domain.
"Um, no. That would not be the scenes a faire doctrine."
The scenes a faire doctrine, which I don't have to google for, thanks, permits people to copy without fear of infringement, stock elements from works, which are typical, if not indispensible, for works that have a particular setting, genre, theme, etc.
In this case, where you have a show about teenagers fighting monsters with martial arts and giant robots, it would not infringe if you had a five person team, each member of which had personalities as described above, and where the members of the team were color-coded. It's simply expected of the genre, and therefore fair game, even if you copied it from another copyrighted work.
Now if the specific thing you copied was a very detailed example, and you kept all the details, you might then have a problem. So it depends on how much Power Rangers embellished on this standard device, if they did, and if so, how much of that embellishment, if any, was used in this case.
If you disagree as to my explanation, please feel free to actually say what you think the scenes a faire doctrine is.