It is no wonder that Palmer units are so popular especially in live situations. For example Palmer PDI-09 is basically a low pass filter set at 5kHz. The low end gradually and very slightly rolls off from 200Hz to 20Hz. It also doesn't have the bump at around 150Hz that regular guitar cabs have, so it may sound a little bit lighter when palm muting etc. It may sound dull and blunt when played at home but it works with a band very well. Also, the Palmer's eq curve is more like a straight line, compared to the eq curve of a miked cab which is jagged with peaks and valleys. So the sound, while not being so authentic, is more full.
In my opinion it is the mid content between say, 600Hz to 4khz that are crucial for a fat sound and cutting trough live. Many profiles are too scooped in that area for live playing.
In studio one will use whatever sound that is suitable for the track and double or triple tracking guitars may need more high end than a single guitar. Plus the guitar sound has to leave room for the vocals etc. But for live sound, the "frown" curve eq is the way to go imo. In other words, guitars slot in band sound is in the mids, whereas the lows and the highs will be washed away once the band kicks in.
Listen to profiles made by professionals with lots of live playing experience, for example Michael Britt or Bert Meulendijk. Those guys' profiles have ample of mids and not too much piercing high end or boomy lows, so they work live very well.