I always find these discussions about bullet performance, difficult discussions, because there are so many variables at play, and so many unknowns in the discussions. Invariably, I wonder what expectations the bullets are intended to meet?
One such critical variable is the speed at which the bullet is designed to be used. In the case of the original non-bonded .375, .450/400, .450, .470, .500, etc. DGX, these were bullets that were designed to reproduce the construction and performance of the original Kynoch slugs, in order to regulate in doubles that were regulated with Kynoch ammo, and in order to match the ballistics of the multiple rear sight folding leaves calibrated to specific distances on classic "express" bolt action rifles.
I have always wondered if the issues reported arose from factory loaded ammo, or from hand-loaded ammo in which the bullets may have been pushed outside of their speed envelope. I generally do not know the answer, because rarely do folks who experience an issue provide such information, but, for example, I would not expect a traditional "soft" bullet that was designed to be used in a .450 NE load at 2,150 fps to perform well at .458 Lott speed. Is there a gap in expectations here?
Another variable is the definition of "failure". I would think that we all agree that game reaction to a hit is hardly calibrated on a constant scale. Some Buff go down at the first shot, some go down at the 10th shot ... or anything in between, and this seems to happen regardless of which bullet is used. Does a bullet fail if the Buff does not go down? I am not sure...
As mentioned in my previous post, there is also the question of what constitutes bullet failure? The old question: "at which time in the animal death did the bullet fail?" always struck me as pertinent. I have a lot more experience with the Nosler Partition than I do with the DGX, and I have lost count of how many mangled NP I recovered from stone-dead game. To push the point further, the NP was in fact DESIGNED for explosive expansion of the front core, and yes, many recovered NP have lost most or all of it, and do not look good in postmortem pics, but they are recovered from game they killed, and they met perfectly the expectation placed in them. Is the definition of success for a bullet to produce a book-perfect postmortem picture of equally and evenly mushroomed petals? I am not sure...
Does a 1945 technology NP fail because it does not look, post-mortem, like a 1984 technology bonded partition A frame? I am not sure...
Does a 1910 reproduction technology DGX designed to duplicate the performance of a Kynoch in a 1920's classic British double fail because it does not look, post-mortem, like a 2020 technology TSX? I am not sure...
Does a 1965 Mustang GT fail because it does not match the performance of a 2015 Mustang GT? Or would the expectation that a 1965 can outrace a 2015 be unreasonable?
Just because we now benefit from bullets that - in most (but not all) cases - perform equally well at 1,800 fps and 3,800 fps, and that - in most (but not all) cases - retain fairly reliably 95% of their weight while exhibiting a beautiful harmonious mushroomed shape and/or delicate petals, does not necessarily mean that other bullets that do not, fail. It may simply mean that older technology bullets have a narrower window of performance, and that wise hunters would be well served to use them for what they were intended.
Obviously, there have been, historically, some flawed designs, well documented in the literature, such as various "copper capped" designs that not only gained disastrous reputations, but also stained forever the calibers to which they were associated. The 10.75x68mm Mauser comes to mind. But this is not what we are discussing here.
I do not know, but I could understand John Nosler or Steve Hornady sticking to their gun (pun fully intended) saying that the bullets they designed perform exactly as expected, hence flawlessly ... in their expected application.
It is of course obviously smart to prefer modern-design bullets that perform across a wider performance window when the rifle used launches them well.