How am I supposed to separate Jean from the Phoenix when the Phoenix always acts pretty much like Jean is its one true pair?
Because for most of Jean's history, she didn't have access to the Phoenix Force? It prefers her as its ideal host, but it's abilities and her abilities are separate things.
And on what grounds do we qualify that the Phoenix is less powerful than anything else? I mean, how do you judge something as "more powerful than" something that can rewrite time-lines, exert influence over entire universes, and holds the power to instantly end and rekindle lives in a single moment? In the original Dark Phoenix saga, it's described as "God-Like" by the Watcher, who adds that, had she lived with it, Jean would have become a "God". The Watcher added that in her current state, she was already able to make her thoughts into reality. He says her power is second only to The Creator. A power with which she has become one.
And that was BEFORE she became the White Phoenix and BEFORE she was reaching out and altering timelines and universes.
Calm down son. I said this because there's an established cosmic heirarchy (per marvel) already in place.
Originally (back in the 60s) the top of the food chain were death, eternity, and galactus in between to balance them. Everything else was lower. It's since been expanded a bit, but I'll get to that.
And you'll notice I said in terms of what the PF has actually done
on panel, it's not that powerful. As you said, the Phoenix even back in the day was scared for it's life, and running from the Shi'ar. The higher abstract powers are impossible to destroy by conventional means, as they use M-bodies and actually exist on a higher plane.
Everything the phoenix has ever done, including timeline manipulation, has been outclassed by a cosmic cube. Those things rewrite universes entirely at will, depending on the strength of the user. Thanos used one back in the day to merge himself with all existence, and become god. Essentially, everything, everywhere.
POST Secret wars (that is, After beyonder was massively powered down) The fight between Molecule Man and the Beyonder was wrecking the multiverse. Turning 2 dimensional realities into three, striking watchers blind, giving life to the unliving...as a
side effect of all the power they were throwing around.
and yet both of these two have only a fraction of the power of a full cube. At some point cubes "mature" and gain sentience. Kubik and Kosmos are two of these. Thanos (who again had used the full power of a cosmic cube AND the power of the infinity gauntlet, described that power as "limitless."
And yet...even though that power is infinite, and allows them them to warp the laws of space and time at will, it is "as nothing" compared to the power celestials hold. There are "levels" to infinity within the MU, and even the "infinite" power of a cosmic cube, enough to warp a universe at will is low tier.
The Phoenix force is one of many essential, enigmatic forces within the MU, and not even the strongest. It's power was countered by the Dragon of K'un Lun sometime in the past (per AvX, going on now) and prior to that, the Goblin Entity of Earth 1298 consumed it entirely, going on to consume and devour the entirety of that reality until stopped only by the fifth celestial host.
Celestials are beastly. But their power is STILL less than that of the Abstract, essential forces of the universe such as Eternity/Infinity (who in some cases is stated as their creator, though this varies) Death, or a fully powered Galactus (the 616 "prime" galactus is stronger than the other variants- only that one has the nullifier, in case the scan above is confusing).
And THOSE entities are weaker still than the combined power of the infinity gauntlet, which is itself below the power of the living tribunal, which serves the one above all. THAT's why I said the phoenix in the grand scheme of things is "not that powerful." In terms of what it can do and has done, it's vastly outclassed by the higher powers.