Are fandoms religion substitutes?

[Agonized-Statism]

No. Were fraternal organizations religion substitutes? How about neighborhood associations? What you may be noticing is that they're all social organizations. That's the social aspect at least. On following the canon of a certain piece of media, more people may have more free time to pursue that now that discrimination against the irreligious has declined to a point where it's normal not to go to church, but I wouldn't call it a substitute. It's not the same appeal as following religious texts, which theoretically address anxieties over the meaning of life and promote virtues.

Unless you're super religious, and anything that doesn't have religion in it is a distraction from God (in which case what are you doing here?), then no.

[Agonized-Statism]

This is also the purpose of many secular works of fiction, no? It makes sense that folk might develop similar attachments to those works and model parts of themselves on it (writing smut about it is another matter, though). People have an intrinsic urge to identify with aspects of the world at large greater than themselves, and it's from that impulse that we have totems, gods in human forms, and groups centered around interests like these, especially given the contemporary culture of intimately identifying with fictional characters.

Maybe for some people, but as a pretty intense fan fic and fan art maker myself, not really. It's catharsis and wish fulfillment.

[Agonized-Statism]

Faith is also a source of "catharsis and wish fulfillment" for many people, myself included, but I don't want to stretch this comparison beyond its usefulness.

It sounds like this is such a broad comparison that anything could be considered a religion substitute.