Different strokes for different folks.
To me it's the Throatiness of a 15 that i like at times . NOT the Bottom..
I have played 12 cabs that have Much more bottom extension than many 15 cabs that are out there... It's not the bottom for me.. In fact , there are 10s that put out more bottom.
.. Currently for the work that i do, i don't need hifi.. I need Clean power , and like my rig to have a little of its own personality. ..
A 15 that has a smooth top roll off has a different FEEL and attack in the Throaty mids than a 12 does.. Maybe it has to do with beaming at higher freqs???..Some people may hate that but others may find a sweet spot and be in Nirvana.. But i find 15s (tweeter or none) Great for some Rock stuff , Blues, RnB , country etc.. . I think its the way that i hear it..
I have never been a fan of 410s or 810s. Just my taste.. .And have not been a fan of them for many many years. .I had No Idea the scientific reason until i started reading stuff on forums over the past 10 years or so.
To me many 410s and 810s have some serious Comb filtering .. I always heard it, but didn't know what it was or why i didn't like it.
Many Rock guys wind up Boostig too much treble to over compensate for that comb filtering in 410s and 810s . I think that adds to that scooped sound that isn't really my thing.. I often gravitate more towards a single 15 a pair of 15s because they are stacked vertically, sort of a LINE ARRAY.. . And always sounded less convoluted to me..
Im currently still running one or two Genz Uber 115s . I Modded them with a little more internal Damping which smoothed the mids and made a great 115 sound even better. One box is loud enough to use as a monitor on arena size gigs.. FOH of course.
I use 2 of them stacked on my Guitar hero gig.. And times add one more cab when guest guitar heros are on board.
In reality One would do 90% of the time though
I was for decades until I hear a properly tuned Faital 12" driver. One can close their eyes and not know it is not a 15. I A/Bed a 15" 3015 and the Faital 12 just to hear the difference in low end. Low end was close but the Faital was easily perceived as more efficient. Some of this could of course be cab design, but I am a 12" convert after playing nothing but 15's all my bass playing life of about 45 years.