After the NMS fiasco, I'm pretty sure that was a one-off.
I just researched another niche game that I recently bought, Nier: Automata, and it "only" has 3.5 million sales so far, yet is considered a huge success. There are a couple of differences between Nier and Elite - first, Nier is rarely on sale, and even when it is, it's still not "cheap". Second, AFAIK Nier does not have to support a vast server infrastructure like ED's BGS requires. That said, I guess 3 million is still a worthy accomplishment after all.
Well, yeah. Nier-automata has been a hit, topped the charts at launch, received plenty awards etc. Its been a massive success with 3.5 million sales.