IMO putting an important number in your post/comment, and not providing a source for that number, is also kind of low effort. If you verified the number before writing, you already had the source ready and you could just put it in the comment. If you wrote the number from memory, not checking if your memory is correct is low effort (but you can also warn the readers that the number is from memory, that's better). If you're intentionally misrepresenting what the number means in your comment (and giving the source would contradict the meaning of your comment), or just giving a number that "feels right" or a number that you know is wrong, then it's low effort and a lie.
I try to verify important numbers and facts in what I read, and seriously, there's so much fake or misrepresented info everywhere, on every political side, that it's depressing, and it makes me don't believe literally anything without a source, unless I verify it myself. Of course when someone provides a source, I often look into the source, and sometimes it turns out that the text misinterpreted/misrepresented the meaning of the source. On Wikipedia, I also check if what is written is actually in the source, because sometimes the editor writes his own opinion while only loosely basing the text on a source (or basing it on nothing).
Verification can take some time, and that's the effort passed from the author of unsourced claim to its many readers, unless they just trust it or ignore the claim.
When I write anything I try to include sources for important things. If I wouldn't include a source, and someone asked "Source?" I wouldn't think "what an annoying guy", I'd think "oh, I could have linked that in the first place". And I usually upvote "Source?" comments (unless it's a thing that anyone can check in 30 seconds). I usually double-check the facts in what I'm writing, and many times I almost wrote something from memory that wasn't true, but looking for a source saved me from that.