Had same opinion, but i thought my brain might need to adjust to flat sound. 2,3 days passed and i felt nothing lacking anymore.I have the 8351b's and my experience was similar: the GLM-corrected response, prior to my using the Sound Character Profiler, was too flat - lack of sufficient bass and a bit too bright from (at least in my perception) the upper midrange through the treble.
I was initially surprised and dismayed that the SCP Low Shelf boost is capped at 3dB, because all the target curves I'd seen online seemed to employ a low shelf boost of 4 to 10dB. However, I found that 3dB was sufficient, in fact my boost has been between 2.5 and 2.8dB for the 2+ years I've owned the speakers, and I've never felt the need for any additional bass. I have periodically tweaked the the cutoff frequency within the 100-200Hz range, which I find makes a bit more difference to me perceptually than tweaking the low shelf's amplitude. (Of course the amplitude would make more of a difference if I changed it by 2dB or more - I'm talking about small adjustments here.)
Even with the high shelf, where there appears to be no such limit on attenuation, I'm only about 1.8dB down, whereas a lot of the online target curves appear to be 3-6dB down.
I suppose I could just have abnormal preferences, but as far as I know I like tight, powerful bass like most folks; I'm definitely sensitive to excess treble and find it fatiguing; and while I do lean towards a more "revealing/analytical/clinical" sound as some audiophiles like to term it, I definitely do not like excess "leanness" in the 100-250Hz range.
I have no explanation for why my +2.8dB, -1.8dB low-high shelf curve sounds just dandy while I previously used something like a +6, -3 curve with Dirac and other similarly full-range speakers, but there it is.
Oh, one final note: I've been struck in general at how audible even small changes to the low and high shelf settings can be. I have found, for example, that a shift of the Low Shelf cutoff frequency downward by 20Hz, combined by shifting the High Shelf cutoff frequency upward by 100Hz and changing its amplitude from -1.9dB to -1.7dB produces a subtle but in my experience very clear difference in the overall sound profile.
Of course it could be confirmation bias/placebo, but for what it's worth I don't detect this difference by leaning in and focusing hard aka "critical listening." Rather, I notice it based on an almost physiological response - it's like the sensory impacts of "warmth in the bass" and "presence and bite in the vocals" are rejiggered just a little bit, the balance between them changed slightly. I understand that even such a "gut feeling, I really wasn't actively listening for it" response could still be confirmation bias. My hypothesis, though, is that because shelf filters have such wide bandwidth, small changes in them can have an fairly easily audible effect.
Curious as always to see what others might think about this.
Later tried to add couple db of bass, but i didnt liked it how it made sound slightly slower and tinny bit less airy.
For me atleast, slightly colored fr is better on 1st impression, but when you give it time, your brain can adjust to flat sound.
For movies i love to add 3db bass though.