It's all about execution isn't it?
Generalizations are tough, but there is a lot of sensitive music content between 150 Hertz and 800 Hertz - like vocals. Cello is always so telling in this range as well. I never said that NO 3-ways can accomplish a smooth transition in this range, I said "I shy away from" loudspeaker designs that place a crossover point in that region. Why? Because I design and optimize loudspeakers and I can usually hear that transition, and the differences between the drivers in the crossover range are often noticeable to me and often spoil my listening experience.
Yes, of course. There are enough speakers out there now with great execution that I don't think it's worth bothering with the ones that don't even have that. So to me discussing design pros/cons is only worth doing in the context of well-executed examples, the rest is not even worth typing about.
The biggest issue with the Genelec 8361B is that the lower frequency distortion increases substantially at only 98 dBA per Amir's review. That means they do not handle as much power, nor play as loud and clean without distortion as some other speakers using discrete drivers.
The 8351B have a -6dB point of 32hz and a woofer area of roughly 8.5". They're not a very large speaker. Considering the 32hz -6dB point, the SPL and distortion are good when compared to other speakers in the single ~8" woofer category. For playing loudly without subs,
that would be the 8361A which has a ~10" woofer and plenty of power. Not reviewed here yet, but hopefully soon!
On the other hand, if like me, you consider subs and multi-channel to be a requirement for your system no matter what speakers you choose, then it's less of a concern.
The people going "gaga" over the almost century old technology of coaxial drivers are people just like you that read advertising copy about "perfect point source" drivers and perfect imaging, but who are in fact inexperienced at loudspeaker design and just parrot such advertising copy.
It's not about fundamental technologies, as you said, it's about execution. That's what people are going "gaga" about. So far we haven't really seen well-executed coaxial designs from any manufacturers except for M.E. Geithain, Kef, and Genelec (bonus mention for Kali and their IN-8, though it still has some flaws due to the low price point). Examples from older manufacturers like Tannoy have proven to be poorly executed.