NS10s sound a little harsh in the mid-range and brittle on the high end. But, you can discern all the frequency ranges (except the low end, where they roll off and need to be filled in with subs) with great precision (for the era).
The reason for their good reputation among many was their accuracy and pervasiveness. The reason for the poor reputation was their fatiguing harshness, making them less comfortable for long mixing sessions. Both can be true; we can recognize the good and the bad.
They sound REVEALING. That's not the same as 'good' or 'accurate'. I'm not contradicting you: you can discern all the frequency ranges, and all the tones, and the things you did on other speakers that people complained about in your mix and you went 'but, but, I did a really good mix!' and then you listen on the NS10s and the complaints you got are suddenly right there staring you in the face, so you can't miss 'em.
That's largely because of the exceptional time-domain performance as the article correctly reports. These are not the only speakers that can do that, but they're really good at it. That plus the harsh mid-emphasis and brain-fryingly bright tweeters means the things are ruthlessly revealing. Accurate would be more sympathetic to good mixes and let you slide, but NS10s are merciless and you must get things exactly right: in mixes, in getting sounds, in auditioning things like plugins.
That said, I think there's a temptation to exaggerate. A phrase like "brain-fryingly bright tweeters" means something completely different to someone who isn't an audio engineer than it does to someone who's worked in studios or dealt with pro gear. NS10s, while harsh by studio monitor standards, are likely indistinguishable from other mid-range speakers of the era to the average listener. The difference is small, and only really becomes an issue with extended critical listening...8 hours sitting dead center in front of these speakers does feel brain-frying. But, a casual listen wouldn't reveal that. They'd sound like punchy, bright, tight, speakers. Which is what most studio monitors sound like to untrained listeners.
Which is why I'm kinda shaking my head at the comments here saying that NS10s sound "terrible"! It's just not true. They sound like what they set out to make them sound like. And, most importantly, the resulting recordings that came out of more than a decade of market dominance speaks for itself.
They aren't terrible speakers. They were a pretty good quality professional tool used by many professionals for many years to excellent results.
Once you use them you are kind of stuck. Your ear gets use to them and you mix to them. You can go to several different studios and you can mix easily. The idea is that the sound that comes out of the speakers goes directly to your ears and not reflexive sound. I have 1030a and they are small but I can mix in bad acoustic rooms and still have a great reference. You can plug any speaker of theirs into any of their sub woofers and have the same reference sound. So the use of Genelec has been growing and have become the standard. Sadly they aren't cheap but they are worth it. Mine are almost 20 years old and they still are great.
There are ATC, PMC, Amphion, BareFoot, Unity Audio, and many others that all sounds more revealing and better.
Though they seem to be big in broadcast studios and post-production places or those where people haven't auditioned a large number of monitors.
I don't know much about professional audio, why these are good speakers?