I just bought a pair from Amazon for $88 to see what the hype was all about, and I don’t see how they can be called bright at all. They are very warm (not a good thing), even dark, just like how the downward right tilt in the frequency response graph indicates. They have no air, no sizzle. I’m comparing them to my NHT C3s, which sound far brighter (I love them!).
That downward tilt is the in room by the way, if a speaker measures flat anechoically and has fairly even off axis response it will be a downward trend in room. So an in room downward trend does not by itself indicate a dark speaker, although it may indicate that if the trend is severe and depending on the dispersion character of the unit.
I had the C3's which I found are on the brighter side of neutral. It is perfectly fine to love them and I also liked them but they are not exactly a truly neutral comparison IMHO.
I also felt the Sony's were a bit darker in my room than some other have suggested and more rolled off then the estimated in room response in the review, though not fully a dark speaker.
The Sony set does fall apart audibly as the volume is turned up to loud. That may also contribute to a sense of brightness for many with added harmonics and non harmonics( distortions).
Brightness is not always just associated with the high treble response, the Sony does have a somewhat peaky response which may be an issue for some listeners.
Whilst these are probably good value for money, I can't help but think that the two tweeters are unnecessary..
Personally, I can't even hear past 17.5khz, not sure about the rest of humanity though.
The speakers were designed to sell at a low price in as many mass market retailers as possible and often to buyers with a very limited education in audio.
It is probably an okay compromise between engineering and marketing. These need to sell in the 10's upon 10's of thousands to make sense for Sony, which by itself is something very few speakers can ever do.