I have a few thoughts on this.

First, it's definitely worth considering if you're contributing to conversations, but as others have said, I don't think the bar has to be "your post is as well-thought-out and detailed as a Scott Alexander post on the same topic". I basically trust the Forum's karma system + people's own judgment of what's valuable to them to effectively filter for what's worth reading, so I don't think writers have to do that themselves. If your post isn't valuable to individuals, they won't read it or upvote it.

A way you can see this is: if you write the thing, people can choose not to read it, but if you don't write it, they can't choose to read it. I feel like what you are doing is similar to how some EAs are like 'oh I won't apply to that job because I don't want to waste the org's time and surely I'm not a good candidate'. Well, that's true for some jobs, but most orgs want people to apply, even if they are uncertain, and they'll do the filtering themselves! 

Second, maybe if you're worried about diverting traffic from posts you see as better, you could incorporate those posts into your own and link them/give them a shout-out.

E.g.: [at the end of the post] "if you're interested in this topic, I found this post by [NAME] super helpful in clarifying my thoughts."
E.g.: [at the start of the post] "I really enjoyed this post by [NAME] on [TOPIC], and it inspired me to write up some more arguments about [TOPIC] that [NAME] didn't go into"

i.e. frame your post as a "yes and" or as a contribution to an ongoing conversation, rather than something designed to compete with, or be as good as, other posts. 

NON-example: "If you care about this topic you should probably read this post whch is waaaay better than mine I'm sure" self-flagellate, self-flagellate

Third, would it help to frame your writing (to yourself, or explicitly in the post) as a way for you to clarify your own thinking, rather than as something that has to make an original argument? For example, Holden Karnofsky has talked about 'learning by writing': maybe you are doing a version of that, rather than being at the absolute cutting edge of research. You might say 'well, in that case, I don't need to publish it', and it's true you don't have to publish anything, but some reasons to publish this sort of writing might be:

-it might be helpful, not for experts, but for others with similar expertise to you (or less) who are trying to clarify their own thinking on the matter
-you can get feedback from commenters that might help you learn
-the fact of having Published a Thing might motivate you to do more of this


 

I think there can be multiple benefits for apparently redundant writing:

1. Bringing more attention and interest to a topic, creating more space for discussing it
2. Having alternative write ups that are more accessible/attractive to some people, because people have different preferences over writing structure, styles, lengths, etc.
3. Identifying areas of disagreement or things to refine, red teaming
4. For your own understanding, to learn more about the topic and get feedback from others

But I do expect diminishing marginal returns in the benefits from others reading your work the more "redundant" it is. If you're aiming for impact through influencing others with your writing, you should keep in mind whose behaviour you want to influence, what you could accomplish by doing so, and how to best do that with your writing.

This is how I felt when I first tried to write for the EA forum. In order to know what kind of text is needed, and what would be new in the topic you are writing about, you kind of need to know everything that was already written and what sort of stuff would influence decision-makers. It’s impossible to know all that for someone new to the space. This is why I think it’s useful for senior people to suggest very concrete topics to junior researchers and then to guide them. And especially for the first few articles, the more specific the topic, the better. I think this article has more advice like that.

Very much empathise with this! 

You might find this thread helpful for ideas of topics which people on the EA Forum would like to see, and haven't seen somewhere else. 

I'd also reiterate a theme which is in other answers: If something is worth saying, it's worth saying more than once. And, even if you find another piece of writing which covers the same idea/ problem, your approach will definitely be different to theirs. You might not be best placed to know what is unique and insightful about your writing, so, if in doubt, leave it to the audience. 

PS- this reminds me of a kind of analogous thing in music; when a band finds a really good riff, why don't they just make 30 songs with it? I know some bands that have sort of done this, and authors sometimes do it when they create really good characters (with book series). But often musicians and authors don't, perhaps because they want to be authentic, or keep moving forward. But who's to say that that riff wouldn't have been better in another song? And now we are locked into a path where it can't be used in one. Let's not do that with ideas. 

There are other goals you could adopt. 

To learn and develop your own thinking. If that's your goal, it doesn't matter as much whether you share it, or the reception it gets. 

To share important ideas. If you're absorbing a lot of your content from the EA forum, try writing somewhere else. Other people may not have been exposed to these ideas, so you might be able to do more to improve the average quality. 

My personal hot-take is that most people should write for a different audience than than themselves. My own ideas often feel stale and obvious to me, while what I consume is fresh and interesting. But occasionally others' have commented that they love my writing (and I don't hear from the one's that don't like it all that much).

Here's my advice, if I may. If you know that someone's already written on the topic, but you're still hesitating as to whether to write it or not—instead of abandoning it without a second thought—then I assume there's something that you feel is still worth writing; as you say, "I acknowledge that I might have some novel ideas and something to add." Or perhaps the way you look at the issue, the way you express it, the way you summarize it, the particular point you emphasize, etc.

I mean surely, if you really thought that someone else has already written something that sufficiently matches what you're about to say, you wouldn't even be asking this question, no? 

As for the sense of "overwhelm," no I don't feel it. I appreciate well-written posts, but as far as I could tell, this forum's guidelines do not include any requirements to either "refraining from already-discussed topics" or "making brilliant posts all the time." So why self-impose further requirements? You have ideas, so you should express them within the bounds set by this platform. Go for it!

write, write, write.