IMHO, it's the imperfections of the JBLs as great mix monitors , that make them great for driving modelers. Mine have always been with the tweeters at ear level. Their near field-ness isn't quite as tight as a better monitor.
Genelecs are a killer product, maybe too good for that application.
I have sets of the 1st gen 305s and 308s packed away, I guess I should sell them at some point.
I could see that.
With the 305's, they were pretty uninspiring for modeler use, I think because the treble is a little more forward and the mids were kind of scooped. So it always sounded like playing guitar through a hi-fi speaker which wasn't at all a good thing.
Here you can see with measurements from ASR, there's a dip in the mids from 200 to 800 Hz (hey that's where all the musical notes are), then a lift in the treble from 1k on up.
On the flip side, the 306 to me sounded quite warm in comparison, but there is detail. I think it's mostly due to a dip in the upper midrange right at the crossover point, which is a common complaint, and it makes them lose some clarity and detail. But that's also where harshness can be an issue for guitars. Still, they are really flat from like 60 Hz all the way past 10k, flatter than the 305's for sure:
That really bears out what you found as well, that they are good for modelers because they are pretty flat but laid back in trouble spots. So you just want to turn them up a little more.
I find that the more revealing and forward the monitor (or headphones), the more potential issues you have trying to find the right IR. And that sent me into a spiral for years looking for the right IR or modeler. But I think it's much more an issue with the monitoring, which I should have damn known.
Here's the Genelec 8020's:
Seems like for very close monitoring they are going to have a little more treble, but with some distance it's better. And there's little low end too, in a perfect room I think they would do fine especially with a subwoofer, but I am definitely finding there's a lack of lows below 120 Hz. Where the 306's even in a crap room are playing fairly low and they sound nice and punchy.
This is super long winded and off topic, but this is another really interesting experiment for me. I always assumed that unless you have a good room and it's properly treated, you may as well just use smaller flatter speakers. But I'm definitely hearing that large speakers are much better at least for playing guitar.