I'm surprised imgur still exists. It's been years since reddit started doing their own image hosting, and that was basically the only thing anyone used it for.
I don't really use either sites, but isn't Reddit mostly a collection of links to content from other places? Whenever I needed to share an image online over the years, I tended to use Imgur without an account after bildr.no shut down, but I did only use those services if it didn't matter that the image disappeared after I'd shared it, and now that you can copy-paste images into basically any messaging service on basically any device that sort of need has disappeared.
Of course, some of them use NSFW tagging for spoilers …
Yes, to my knowledge, you are correct. It was a surprise when I first learned it but apparently there are users that visit imgur directly without using reddit.
Not really. Even the most popular posts on the imgur front page average around 1,000 upvotes (compared to 40,000 for the reddit front page with default subs) and most are only getting 300 upvotes with 20-30 comments. That's about as popular as a middle-tier subreddit, of which there are thousands. Which I guess isn't "dead" but those certainly aren't numbers that are going to get the VCs opening checkbooks.
Measuring active users for imgur is tricky because a massive proportion of those users are just using it as an image host and not "engaging" in the community. And even a lot of that engagement is just being driven by Reddit rather than coming from imgur itself.
So no, I think calling imgur a popular social media site is extremely misleading: it's an extremely popular image host that happens to have a social media site that a small community uses attached to it.
For months now, I've been unable to view photos on Imgur. Only recently, I finally realized their "over capacity" error was their cop-out for "we don't want to serve your IP blocks". (Yes, I am primarily on VPN.)