Filtered or not, it is not difficult to sneak something past the YouTube algorithms. Why just recently we had that lovely scandal about cartoon characters that only demonstrates that.
Yes, but those are easily reported, both to Mods here and to Youtube, so there’s two different teams that could take it down, which means it’s likely to be taken down rather quickly. (Honestly, any NSFW thing I’ve ever seen on youtube never survives more than like 20-30 minutes in my experience)
Whereas you can’t report NSFW images to Imgur, because they aren’t against Imgur’s Terms of Use.