Y'all, don't shoot me! lol! Butterflykyss is engaging me in discourse and I'd be remiss to ignore their replies.
I think I stated what feats pre-downgraded Phoenix accomplished, but I will be more succinct: 1) She resurrected herself after the shuttle crashed in Jamaica Bay (Claremont makes it clear that she died, became an entity of pure thought, and then reformed as Phoenix); 2) fought and essentially defeated Firelord, and 3) repaired the M'Kraan Crystal. Again, Ororo could not accomplish any of these feats.
Better still, Claremont neatly summarizes this—what you refer below to her "interim step"—in the following panel from Uncanny X-Men #125:
Mind you, as the panel above suggests, Claremont didn't really depower Phoenix as much as have her burn herself out after repairing the M'Kraan Crystal. This is equivalent to a runner completing a marathon and then being exhausted and unable to immediately complete another marathon after, i.e., the runner wouldn't be permanently burnt out, only temporarily.
And, again, you are ignoring the following quote from 1979 in favor of the quote from 1982. (Mind you, the first quote was from an interview Claremont gave before the Dark Phoenix Saga was even published; the second quote is from nearly three years after its publication. Needless to say, I trust the accuracy of the first quote more, since it was closer to the time he created Phoenix:
"So, anyway, we were told, Dave and I, that Phoenix could not be cosmic....We had to cut her back. So we decided to cut her down to roughly where Storm is, which is fine.”
I explained what Phoenix's "interim step" was above and also that, while Phoenix was "burnt [...] out," she wasn't permanently depowered, as evidenced by the fact that she would go on to become Dark Phoenix.
But you've been claiming exactly this, even though I've proven that this is not true.
This is incorrect. I will reiterate that the following Phoenix feats Ororo could not and did not accomplish: 1) Resurrecting herself after the shuttle crashed in Jamaica Bay; 2) fighting and essentially defeating Firelord, and 3) repairing the M'Kraan Crystal.
It can be said that Phoenix was reduced to Ororo's power levels after her M'Kraan Crystal feat, which, in fact, is exactly what Claremont states, leading up to her transformation into Dark Phoenix, at which point her powers surged again.
I've sufficiently explained above when and how Phoenix was reduced to Ororo's power levels. To be clear, between her resurrection from the shuttle and repairing the M'Kraan Crystal (From Uncanny X-Men #101 to #108), she was considered a cosmic superhero and more powerful than Ororo. That is precisely why Claremont decided to, as he stated in 1979, "cut her down to roughly where Storm is." If she had been at Ororo's power levels all along, he wouldn't have needed to "cut her down."
And Jean being classified as having "infinite mental powers" happened way in advance of the creation of Phoenix.
Oh, I agree on this, but again, I stress: Jean was classified as having "infinite mental powers" in 1968, shortly after Xavier awakened her telepathy, which she was able to use to track and psi-scan an "electronic [robotic] brain." That was nearly ten years before either Ororo or Claremont came to X-Men.
Again, you are not only misinterpreting or misrepresenting (I can't quite tell) Claremont's statements—he clearly states he "cut her down to roughly where Storm is"—you are ignoring the fact that he was not the writer who attributed "infinite mental powers" to Jean. Again, that happened nearly a decade before he became the writer for X-Men. At best, he chose to further explore this by making Jean evolve into Phoenix. Jean having "infinite mental powers" never came about because of or was dependent on the Phoenix Force.