Interesting. The only work-around I've found for the low-end loss I've experienced is to set the UD so it is WAY louder when engaged. Otherwise, it disappears on me when I try to use it for a song here and there throughout the night on a gig. Perhaps this is normal when using dirt pedals with no clean blend?
Anyway, I do love the UD for always on OD.
I wish we were able to sit down and converse in person and play with gear, because I'd love to see how your rig is interacting with the pedal. I only have my own experience to draw from. I sometimes use clean blends, sometimes not. I tend to balance the volume on my dirt pedals to unity volume (by closing my eyes and switching back and forth rather quickly) and it's definitely never jumped out as cutting low end in my setup. It might have to do with the level of gain you're using. I've noticed that the low end increases with the gain and I never use mine for low gain OD, I have other pedals that do that sound more to my liking. I use my UD as more pushed, saturated sound, for something like a more fuzzy medium-high gain RAT kind of tone. If you're using it for very low gain, it might be cutting a more noticeable amount of low end. Comparing head to head, I've heard it having noticeably more low end than my OCD, slightly more gain and a "looser" or more fuzzy quality to the gain structure. That's why I still have both, I still like the OCD for a different kind of tone than I use the UD.