the main difference between the X-Files cancer arc and the brief-but-interesting cancer/Mary-Sue arc in the end of the Dellah Benny books — aside from the obvious contrast between Mulder and Scully's relationship having romantic undertones where bennybrax is entirely platonic — is that Chris Carter & co. actually managed to make it fulfilling. there was character and relationship development done via the impact of a main character's illness and possible imminent death.
that's something Justin Richards got very right in Tears of the Oracle, which in a way feels a bit like if you smushed the first and last episodes of TXF's cancer arc (Memento Mori and Redux II) together into one cohesive mass of emotion and character study. not only is Benny's cancer-esque diagnosis in Tears a catalyst for exploration into the inner workings of her own mind in a time when she can't trust it, but Richards also explores Brax's relationship with Benny ("she's like family") and with the mortality of those around him with the knowledge that he will go on when they're gone. the real bummer here is that Mr. Richards left Tears (intentionally?) open-ended, and Dave Stone came in and completely dropped the ball, both on plot and the character/relationship work.
(small aside: I do have a soft spot for Return to the Fractured Planet, despite being MASSIVELY salty about it. it could have been so much better than it was and resolved the Mary-Sue thing so much better tbh. imagine the insanity of having that book be in Benny's POV while she's PEAK unreliable narrator and literally dying. imagine if Brax had actually been involved at all and the interesting meta that could have existed.... we could have had it all, guys)
on the flipside of this, CC & co. not only consistently handled the physical, practical, mental and emotional AND spiritual implications of Scully's cancer throughout an arc that lasted for about a full half-season (including the next season's premiere), they also used it as an opportunity to show how her diagnosis affected her relationship with Mulder over time — he remembered her birthday and got her a gift for the first time only the year she was dying, and his priorities completely shifted from his previous all-consuming goal of discovering what had been done to his sister, to finding a miracle cure for Scully. that's... a lot better than the "are you sure you're okay?" / "shut up I'm fine" exchange between Brax and Benny in RTTFP*. not to mention that the outsider POV in Fractured Planet means that even when Benny is in a coma, we don't really get to know how Brax really feels about it — the POV character doesn't know him well enough or care, so it's irrelevant, which is... a disappointing writing choice, tbh, especially coming after how deeply he was affected by Benny's diagnosis in Tears.
*please note that there are several times that Mulder is overly concerned for Scully and she shuts him down, but in Fractured Planet that's the ONLY direct interaction about it between Benny and Brax???
idk I just think the similarities and differences are.... interesting?? and maybe the fact that, imo, The X-Files did the cancer arc very well, makes my disappointment and saltiness over RTTFP even worse lol. that's... actually kinda the reason I started watching TXF, so. figured I may as well rant about it a bit 😅
