The flaw in the above logic is that you assume that Equinox (or Deus) for that matter has no tells for deep or flat iron which is simply not true. Yeah you will get a high tone, but easy tells include iron grunt off the edge and use of the pinpointer to simply observe you are passing over something too big to be a button or bullet. So yeah, I will dig that iron "high tone" with Equinox or Deus, not because I don't know I am digging iron, but because I want to make sure that iron is not masking something else or is not itself something I might want to recover. One of my best finds was a Deus high tone off the back end of a parrot shell buried 1.5 feet down. Knew it was probable big iron because of the depth for the signal strength, but did not give up on it and was rewarded. People who pass over the "certain" iron are the ones who are risking leaving behind the goodies lying beside or beneath it or leaving behind a spur, projectile, bayonet, or sword blade (big iron can result in a decent relic or lead to a trash pit).
Also, I 100% agree with you that the Equinox TID is compressed, that makes the vdi stable. Similarly, 100% agree the Deus TID is bouncy. But TID accuracy is not a detector attribute I associate with relic hunting but more with coin shooting. Coin denominations typcally fall within nice orderly TID bins, relics do not due to the variety of shapes, sizes, and metals. So I am basically digging anything non-ferrous regardless of TID.
You say you are a relic hunter, but your philosophy to leave the certain deep iron sounding targets and focus on TID, sounds more like a coin hunter. Not a biggie, just two different philosophies on relic recovery here and I get why you wouldn't necessarily think Equinox or Deus are all that. I think it is less, though, about relic vs. coinshooters here (Calabash is almost exclusively a relic hunter) and really less about F75 vs. Equinox either. You approach relic hunting and iron not because of the way your detector behaves but because you would rather bypass iron, period. I get why people line up on one side or the other on certain detectors, and I think it has to do more about hunting philosophies than detector capabilities. My 2 cents FWIW.