I can appreciate your take somewhat. I have two Hel2e's and I do know this units presentation well. But what you've conveyed here is that you are isolating the Magni from the Modi and attributing all of the issues you're experiencing to just the headphone amp. Which, to be fair, doesn't truly tell us which unit is really the culprit.
What you were hearing surely came from the combination of the two units. Just as with the Hel2e, being that it is a combo unit.
I also own both the Heresy and the Heretic and I can tell you - they don't really add to or color the sound in perceptible ways on their own. Not with what you have described. At least not for me.
I have had them both paired with different DAC's recently. The SMSL D0100 and now the Aune X8 XVIII DAC with a SparkosLabs SS2590 dual pro opamp. These two DAC units, in the end, did more to alter the overall sound than the amplifiers themselves. I've never been a Modi fan... So I am obviously curious about how that unit plays into your experience.
The Heresy and the Heretic though can't really do on its own what you are describing. They shouldn't. They will though be very different from the regular, non-opamp version for sure. Perhaps that amp would have suited you better than the heretical versions.
The decoding of the source, that signal - through a DACs topology surely can be altered or colored just how you describe. The SMSL D0100 and the Aune were very similar in their stock form. But still quite different. However, once I started playing with different opamps, Muse02, SS3602, Burson V6 Vivid and then ultimately the SS2590 - that is where things really changed. So my end result sound comes from the combination of both the Heresy/Heretic & my DAC choice. Not just the headphone amp. I'm not saying an amp cannot do these things... But what you are hearing is surely from both units paired together. Not just the one.
The DAC chips inside the Hel2e and the Modi are the same. But their implementation is not. I almost wish you had the ability to try the Magni with different DACs and then give your impressions. That or try the other Magni... Perhaps the fatiguing elements are moreover a Modi thing and not so much a Magni thing - but it might also be a Magni vs Magni Heresy/Heretic thing. We do know the non heretical plays a bit warmer.
On the Magni/Modi front - You could have easily completed the stack by adding a Loki mini+ which would have helped out in the frequency range of things... But not so much with the staging.
On the other side of that..
We can easily develop our hearing to prefer a signature. You really do get used to it. The Hel2e is a great little combo of things and I use it in one system still, as it plays real nice with the speakers on that system. The other Hel is in use by one of my boys. I truly love how that little unit sounds in certain systems. So trust me, I get it. I'm very used to it. Honestly, I think my quest with other gear on my main rig was probably to recapture much of the Hel2 experience, but expand on it if I could. My soundstage is amazing now. Not so much with the previous DAC. Something I think the Hel2e does very well for what it is... The Lokius keeps those frequency woes in certain recordings in check for me.
I'm certainly glad that you settled on the device that ticks all the boxes for you though.