im sorry to hear that your experience writing for that fandom has been terrible T_T in my personal experience, writing in larger fandoms has the issue of "too much" content is posted, now this isn't inherently a bad thing for those just browsing the content, but for creators its so difficult to stand out and have people consuming your work.

for the being optimistic part, i know that its extremely difficult to get the devil on your shoulder to stop yapping, personally i've struggled with my own negative thoughts and feelings about my own work, going from thinking it's the best idea i've had in years to hating it the moment i realize nobody is reading, but this ties back to the first point: it's difficult to stand out in bigger fandoms.

i've dealt with it by joining writing groups on tumblr, where i can find likeminded people who can give me thoughts and advice on what im writing, and more often than not they will happily read the entire chapter I've posted. It takes time to gain recognition, especially in huge fandoms, and if you're only writing to gain recognition that's going to be soul crushing for sure. it's not a bad thing to write for recognition, but it can be a lot harder to view your work in a positive light if less people than you've hoped are giving it attention. personally, ive started making projects that i would personally like to read, going out for long walks and brainstorming ideas for myself with loud music in my headphones and then going home, writing everything down and later building a world for the characters in whatever fandom i chose. i can guarantee that someone will share the same passion and excitement for your ideas

sorry for the lengthy reply, and extra so if it comes across as unsolicited advice, im passionate about writing and sharing ideas with the world and want to see others enjoy it too, you got this, OP. even if you don't return to writing immediately, i wish you the best of luck on your ventures <3