I agree with you in part, but I think the differences can be greater than you'd think. A lot will depend on the particular mix and also the particular playback system and possibly some subjective preference.
In TLJ, the failure to recover ULF from the surrounds is a sin of omission, which is relatively minor. Yes, it does mean that a spaceship might lose its weightiness as it pans from the front, overhead and to the rear, but at least the sound is not worse than what you started with. I picked the surrounds in my example because the difference is quite dramatic on paper and is one that we could all agree would be very audible with those discrete surround effects.
However the front LRC channels are another story. Even though they roll-off at a similar point, their shapes are still quite different from LFE. So an EQ solution that is optimized to the mono sum average (which is dominated by LFE), could introduce new humps or bumps into the front LRC that weren't there before. Here's where we *can disagree* about what's audible and what's not. Though arguing from personal experience, even quite small bumps can be audibly degrading. Much depends on shape and bandwidth of the feature, in addition to the level, and also ...
Audibility of differences will depend on the playback system. Systems with substantial bass problems may not reveal degrading resonances as readily. (That's not a virtue as such systems also fail to reveal a lot of content.) For example, a BEQ filter applied to front LRC that increases ULF while adding a slight bump around 55 Hz may have a pronounced boom around that area in general, but on a system with a severe boomy room mode at 45 Hz, the problem at 55 Hz may be hardly noticed. The BEQ might be an unqualified improvement on this flawed system, but on a system with very clean bass response, the 55 Hz bump may be much more obvious and degrading.
If you had to choose between full ULF extension and balanced response between the deep bass, mid-bass, and upper bass, which would you choose? Personally, I'll take the balanced response over the ULF extension any day. IMO, the ULF is the least important frequency range.
I believe the notion that "[global] BEQ that gives 80-90% of the improvement" is overly optimistic, but I am also inclined to judge the soundtrack for what it will sound like on a revealing system vs. an "average" one. So practically speaking, a global BEQ may be an improvement for most people who choose to use it, even if it does degrade other aspects of the bass somewhat. And I do understand that most people who have EQ capability at all can only use it on the sub output. I agree many filtered tracks can be improved to an extent with a global BEQ and that it's worth doing even if an independent channels BEQ would sound better.
But I'm skeptical that a global BEQ will always be better than nothing at all. Focusing only on ULF, a BEQed track will always seem to be an improvement, but if one considers the sound as a whole, BEQ that introduces new bass resonances in some of the channels could end up sounding worse than nothing at all. Again, a lot is going to depend on the playback system. When doing these BEQs (whether global or channel-independent), it's very important to listen to the results on a system that is as accurate and revealing as possible. (This is probably my biggest gripe with the AVSForum thread where it appears BEQs are being developed using all eyes and no ears.)