Also, would those numbers change much if instead of 14.8V you are measuring 12V? The step up regulator I use is 12V.
The 14.8V is the mains reference. So yes, if you change the reference to 12V then the battery unit would appear measurement-wise to perform slightly better.
I would think running on a layout that really taxes the loco is where the battery idea gets sketchy - steep grades, long helix, long trains, etc. An HO loco under heavy load is going to drain the battery pretty fast. My Atlas 4 axle locos pull roughly 100mA @ 15V when dragging a 16 car train (all metal wheels) on flat track at normal main speeds hence why I used 100mA as reference.
Interestingly I haven't noticed much of a difference when the battery charge gets low. Normally it just runs like normal until it's out of power and then it suddenly shuts off completely.
The LM PWM magic in action. Your loco used in a conventional DC manner would make it obvious the battery is fading away.
Reminds me of a funny battery story. Recently I was working a project that required driving #12 x 4" screws into southern yellow pine. I was using a Bosch 3/8" electric drill for which I had to string 300' of cable to get to power. My buddy questioned why I wasn't using a battery (cordless) drill and started shooting his mouth off about how his DeWalt driver would run those screws all day long. I said bring it over, let's see it. The cordless drove about 30 screws and it was done. Time to swap batteries. I then (with great pleasure) showed him the box of 1000 screws and informed him I was on the second box. I didn't hear anything more from him about using battery tools.