Another big issue you don't want to ignore is doubling....the speaker's tendancy to want to produce frequencies an octave above the one being fed into it. It's a common form of low frequency distortion and it tends to make the upper bass and low midrange sound messy at high volumes. Smaller speakers tend to do this more easily than larger ones. To my ears it presents as a lack of low end EXTENSION. Again, at relatively high volumes. Low volumes...no issue.
I know I've said this on here before, but it's very pertinent here. One time I did a gig with Sanborn at Jazz Alley and Bass Northwest provided an Epifani 410UL. By itself it was unusable...completely unusable. I begged them to bring be a 115 to use with it and it was fine.
The following year I did the same gig, same band, same music, same club, same amp...but they provided a 212UL and it did the job effortlessly. Even though it didn't get as LOUD as the 410UL, it didn't need to. And the projection of that cabinet is stellar in my experience.
I just really like 12's. I checked out a few of Jim's IP cabs when I first built the MPP-1 and fell in love with the 212 IP. I really thought it was great. At the time it was supposed to be discontinued. Did that happen? Of the three I played through, 112, 410, 212, it was the superior by a long shot to my ears.
As we've discussed before, your experience with your one night of using the 410UL is very different from my 1000 or so gigs with one over the last 10 years

That being said, it is very much about the mix and match. I HATED my 410UL with my Walter Woods.... really bad match-up of a low mid hole with a low mid hole. With most other heads, the 410UL can be a beautiful thing for many. I agree with you in general though, the UL line is quite voiced, and it is hard to fight that voice if it isn't your thing.
I greatly prefer the tighter, punchier AE line at this point by a long shot. I've found over the years that an even frequency response in that all important 60-200hz bass to upper bass to low mid frequency response is what defines a cab that sounds even, punchy, deep and not woofy.
I agree, the entire EpifaniUL line has a bit too much low bass extension at the expense of lower mids, and can sound quite hollow (especially the 212UL, which is my least favorite UL cab with most of the heads I've tried it with... pure personal taste there though... it's a fine cab and I did like it better with my Walter Woods, which I think is the head you were using back in the day).
Much of this is about the matching of a cab's voicing to a heads voicing for me, and also the EQ power to 'fix' any issues with a particular cab, whether that is softening the extreme upper mid bite of an AE410, or punching up that 'lack of punch hole' in many of the UL executions.
IMO, and a lot of IME on that one. I am not one who infers much of a voicing difference across driver size any more. I've heard tight, punchy, upper mid grind 115 cabs, and 'subwoofer' like performance from 8" driver loaded cabs, and everything in-between. The variance in tone across 212 cabs is pretty eye opening, from the tight, grindy tone of the Genz 212XLT, to the very wide, pure 212UL, to the punchy as heck TecAmp s212, etc., etc., etc.
Edit: The entire IP line has been discontinued. The IP212 was discontinued very early on. The AE212 is quite different from the IP212... more punch in the lower mids, more grind coming out of the top of the driver, hence a less 'hi fi' sort of top end, and a much tighter and IMO more usable low end. IMO there also!