In order to contextualize my own humble attempt to help (and for the fun, mine at least), let's share a few spectral analysis of humbuckers played in chords, direct to the board.
Below is a hi-gain HB (not a Full Shred but having the same inductance), fitted with an A5 then a C8 magnet. Magnetism is obviously much stronger with C8, which also decreases inductance. Stronger magnetism bumps a bit the low mids but paired with the lower inductance, it mainly makes the pickup noticeably brighter (of 3 to 9dB, depending on the high frequencies considered). With A8, the frequency response should be between the orange and blue line. With A2, it should be under the orange line for all frequencies above 1khz approximatively (IOW: for harmonics).
Now, here is a Hot Rails vs a DiMarzio X2N, which is one of the rare mainstream full sized humbuckers to have almost as much inductance as the Hot Rails. The X2N has three ceramic magnets, giving a wider and more powerful magnetic field. That and the full sized coils + wide rails give a bit more output level and much more bass than what the Hot Rails delivers.
Just to be sure, below is the Hot Rails vs the first humbucker with C8 mag (now in orange). Like with the X2N but for opposite reasons, hard to obtain something more mismatched. The same kind of mismatching is probably what makes the Full Shred apparently "too bright" in the case discussed here.
Finally and for grin, below is something that I've already shared: the response of a same passive humbucker through 1ft vs 50ft of cable (whose parasitic capacitance values are respectively around 44pF and 2240pF). It would be easy to obtain the same response than in the red/orange line from a 2,2nF capacitor between hot to ground, according to the good ol' recipe shared back in the days by uncle Bill Lawrence (RIP, his legacy of pickups designer remains sadly underrated IMHO).
I won't waste our time by discussing to decide if it's a 10% or 90% solution. I won't even claim it's a viable solution for any player who hasn't at disposal the components and lab gear available here and allowing to check objectively the effects of mods. I just know that a capacitor costs a few cents and takes a few seconds to connect from hot to ground of the jack plug at the output of the guitar, if one just wants to try such a cheap trick. Personally, I've applied it more than once. Yesterday at night, I was discussing again with a touring pro for whom I've done it (in a more subtle way than above, thanks to a lower value cap: under 1nF, such a component just tames the high harmonics. Above 1nF, it has a more noticeable effect, not always pleasing and requiring sometimes further tuning).
NOTE - As illustrated by the last pic above, increasing the capacitive load tends to rise the Q factor of any passive pickup. If it makes the sound too nasal, a resistor can be put in parallel with it, making less... peaky the resonant peak (obviously located somewhere around 1.5khz in the red/orange line of the last pic, IOW around the same prominent frequencies than with... the Hot Rails). Again an added resistor should cost only a few cents and a few seconds of experiment.
Sorry for this epic and therefore terribly boring stance: it's Sunday morning, I'm an old fart, I ramble accordingly. ,-)
I wish you all a nice day.
