You continue to discuss the episode as if the story was about the Peter-Alex relationship. It was about the blood worms, (Doomsday biogenic weapons) and the issues about the blood worms, and the relationship was supposed to merely be a consequence of the main plot, as was the Klingon intervention which complicated it. The Klingons show that a crisis is not just a crisis, it effects other ongoing problem, and the death of Alex is no different than a lot of other deaths in TOS, just to demonstrate that the crew is vulnerable, and some people who aren't red shirts with targets on them get hurt and killed. Making him Peter's friend instead of James T.'s friend just avoided giving James T Kirk a new love to lose.
Ideally the show was about the bloodworms, but the choice was made to put the Peter-Alex relationship up front...it's so up front that the biggest scene about it (which is longer than most TOS teasers) comes before the real story actually starts. The relationship is then milked for melodrama.
Not only that, but the theme of the "Phase II" iteration of "Blood and Fire" was about the Peter-Alex relationship, i.e. "Space isn't the final frontier. The final frontier is the human heart; space is where we'll meet the challenge."
Now I don't have a problem with that. In fact, the best stories are about how the characters are affected by what's going on around them. Or how it's often stated in mystery fiction: "It isn't how the character works the mystery, but how the mystery works the character."
My disappointment with "Blood and Fire" is that the execution wasn't what it could've been, and that it TOLD more than it SHOWED, especially since Kirk blatantly tells us the theme of the entire story at the very end.