The differenence between EQ and compression is that EQ is static while compression (can be) dynamic. By this I mean that when you use EQ to cut lows and highs (to give more mid focus for guitar), those EQ setting effect the guitar signal regardless of the volume. Quiet passages will get the same tone shaping as loud passages.
But often, that’s not what we want for guitar. When the guitar is turned down, we want a more scooped tone with low and high end boosted to give a nice full rich clean tone. As we turn the guitar up, and add distortion, we need the opposite: low cut to reduce mud, high cut to keep the distortion from being too fizzy and ice-pick, and mid focused to help make the louder leads cut through the mix.
Now this could be done with a multi-band compressor. You could set the threshold and ratio for the low and high bands to compress more as the guitar is louder, providing the desired mid focus. But this doesn’t work well in practice. Partly this is because there’s likely a fair amount of distortion in most people’s clean tone. This is needed to give better sustain, and add some high frequency content the electric guitar just doesn’t produce and the typical guitar speakers are challenged to reproduce. This is kind of what an exciter does. If you put the compressor before any of this distortion, then any dynamic tone shaping it might do will be partially lost by clipping that comes after the compressor. If you put the compressor after this distortion, then it doesn’t see the guitar’s dynamic range as much and therefore doesn’t have as much to work with, limiting its overall effect.
So the solution might be, don’t try to do this automatically with a multi-band compressor, do it manually with multiple distortion pedals into a clean amp to give you the tone shaping and dynamics you need. Use the gain staging of one to three distortion pedals into the front end of a gained up amp, plus the volume control on your guitar, to get a really wide range of dynamics and tone that are completely under your control.
Where I think a multi-band compressor might be really useful is for mostly clean tones that have a wide (clean) dynamic range. Think of a Strat into a Twin Reverb. You could use the multi-band compressor to tame some of the lows and highs as the guitar volume is turned up, hitting compressor harder and making a more mid-focused tone. But once distortion is introduced, this may not work that well.