If this is you, I honestly urge you to like ... reconsider your thoughts on this? It takes so bloody long to write stuff. Way longer than you might expect.
I write fast. I average 1k an hour. This, as far as I can tell, is much faster than is typical. So lets say it takes me 100 hours to write 100k. Those hours then have to be broken down into what is actually achievable in a day. You can't write for 10 hours every day unless you're on a coke binge. I might do 4 on a weekend day, 2 on a weekday, because I have a job, other hobbies, and responsibilities. Not accounting for rest days or things coming up that prevent me from writing, it might take me 6 weeks to write an initial draft of a 100k story, by these metrics. Then comes the editing. I read everything I post at least 3 times to check flow, SPAG, and other things. This takes way more time than reading a fic normally because you're consciously taking in every word and every bit of grammar. During this, you write your edits and your additions. You might send it to a beta and they then have to take the time to read your fic.
All up, that 100k story probably took 14 weeks for me to complete. And, remember, that is quicker than it may be for most.
Devaluing medium length stories can kill a fandom. Those are your bread and butter, the stories you go back to again and again because you can read them in one sitting. These are the majority of fics. Most fics are not 200k+ and they are sure as shit no less valuable and no less deserving of love and appreciation than longer works.
Not to mention, not every great fic has to be an epic? Sometimes the best stories that give you the most fulfillment are the ones that are about a low-stakes mystery or centre around your ship cooking breakfast or waking up together or just loving each other in everyday situations. Maybe this is an age thing, I don't know. But not every story needs to rip your heart out of your chest. Sometimes the best ones wrap you in a blanket and give you a glimpse at your favourite characters living an easier, more idyllic life than you yourself get to. That's not to say that shorter stories can't make you feel intense emotions, but this is a common argument that I see. I just don't think it's a valid one.
As an aside, most novels are 60k-100k. Nobody is looking at The Hunger Games or Catcher in the Rye and thinking they're too short and not worth the bother. So why do it to fics?