This is the question.
At first a critic felt that I had not done enough research. But it turned out that he had I were using the same dictionary definitions, except that I "equated" two definitions that he thought were rather different.
I also hypothesized a "nuance" not found in most dictionary definitions; that "relentless" was more "honorable" than "ruthless."
Whatever its initial shortcomings, the edited question clearly shows my research and meets at least the "formal" requirements for inclusion on the site.
I realize that my definition may be wrong and the other person's may be right. But isn't the whole point of the ELU site to separate what's "right" from "wrong?" As long as I spell out my assumptions (flawed or otherwise) so that they can be identified and addressed, should my question be acceptable on this site? Or do "flawed assumptions" automatically make a question "poor" and "off topic"?
A defender (with over 10,000 reputation) wrote: "If you just use Google Books or some other corpus and check usage, both past and recent, you will find they are often synonyms. In most cases, ruthless is being used hyperbolically in place of relentless. It is frequently found anthropomorphizing inanimate objects. I completely understand the confusion here. This question shouldn't be closed."
Another high ranked user pointed out that some authorities consider the two words synonyms.(See answer below).
Or perhaps this site is to too "advanced" for my question, and that it is best asked on ELL instead?