The main difference between the two describes completely different things - which is why we have, and need, both. I personally do not use "stages" in listing die varieties on
https://www.coppercoins.com mostly because it would add far too much complexity to the database to do so. It is, however, less accurate to list marker information for simple die states rather than to use the more complex, yet proper "stages."
Two things that come right off the top of my head that profoundly advocate the use of die stages would be a die clash or a change of the opposite die. Either become a very important "happening" to the coins minted, but could not be appropriately described with die state alone, because a die might enter mid die state before a clash, and remain mid die state after a clash, and even gain yet another important marker (like a reverse die change) all while still in mid die state. Markers change dramatically within a single die state.
On the other side of the arguement, dropping die state as a descriptor also would not work. While one die could go through a well-documented series of tragedies during its life and attain enough of a fingerprint to warrant 10 stages, the next die might only warrant enough stages to note the change of die state...3 or 4. We cannot accurately say that any die reaching stage 4 is late die state, because stage 4 in the previously used example may have happened while the die was still in early or mid die state. In addition to this, the attributes or characteristics of an anomaly can change dramatically between die states, so mentioning die state is pertinent to describing a coin.
Die state and die stages work hand in hand to describe two different things that happen to a die through its life of striking coins. Neither is unnecessary - in fact, both are very useful for those who understand them. I saw the article more as a writing of example to educate people as to the difference between the two, and not really an arguement to dismiss either of them as unnecessary.
The science behind this hobby is a world of complexities that have to do with metals, striking pressure, a general understanding of the machinery and how it works, and a keen sense of detail. I am against "dropping" terms and using inappropriate or inadequate terminology to describe observances in numismatics just because some don't want to take the time or make the effort to learn them and understand why they were deemed necessary to begin with. Education and knowledge are the keys to numismatics. We have an excellent foundation set forth by those who first began explaining these complexities in terms that make sense. It would be a travesty to omit or delete their work just because some people don't want to try understanding it.