Another possibility arises. Player B might have enormous natural talent, conceivably even the most natural talent of all time (as the question has been framed by the OP), yet live in an era in which all very talented players study with the best tutors and mentors, play in international tournaments against strong competition and from childhood, study intensively, have the latest in computer software, etc. etc. Maybe his parents even move him to Europe to enjoy the advantages it offers for his chess career....
In that case, how do we know whether Player B's rise to the top is due more to study, practice and cultivation, or to raw natural talent?
Certainly Player B might defeat a more naturally talented but less intensively cultivated player. And Player B might be dominated by a less naturally talented player who had better tutors, advisors, study habits, and other advantages.
But if everyone in the field has fairly equal advantages on the cultivation side, the player with prodigiously greater talent would be expected to dominate.
Caruana was interviewed after defeating Carlsen, and talked about how well he had studied and memorized the opening, and how deeply. And he said that there was no way anyone was going to be able to navigate through that variation well or competitively over the board.
Carlsen may have more native or natural talent, but he doesn't study and cultivate it as much as some others (though he still studies and works and obsesses quite a bit). For the amount of work he puts in, one would expect him to be more dominant if his natural talent were much greater than the competition's. The fact that he is only marginally dominant suggests that his natural talent isn't too far removed from the competition's.
The compass needle still points to Morphy from all the evidence and considerations so far.
In my view, it's very difficult to gauge Morphy's talent. Clearly his understanding of the game was far superior to his contemporaries, but we're talking of the (almost pre-)dawn of modern chess. He played opponents who considered it almost cowardly to decline sacrifices.