The one, and only, thing I will say about 4e--other than to give props to Snarf, because that actually was a pretty reasonable assessment of both what 4e did wrong and what it did right--is to note that it is, very especially, THE edition that suffered effectively zero power creep across its run. Yes, it did have a little bit--especially if you skimmed off only the absolute best-of-the-best options--but given the enormous volume of production compared to 5e, it is a testament to its designers' efforts. By and large, new player options were either pretty much in the same ballpark, only needed relatively gentle errata to fix silly mistakes, or (surprisingly often) were actually less powerful. The vast majority of Essentials, for example, is actually less powerful than what you can get out of the rest of the system! And several of the so-called "weak" classes, such as Warlock and Vampire, had the same top-end power level as any other class, they just needed a lot of optimization to get there, as opposed to quickly reaching 99% power and only slowly gaining more thereafter (as, for example, Sorcerer and Wizard did).
The core point of the above, which is not strictly about any specific edition: Power creep is NOT totally unavoidable. It is, in fact, possible to create a system that actually manages to stay on an even keel and more or less within the same ballpark of balance. You just have to put in a LOT of testing and effort, and you have to know not just what you're designing but WHY you're designing it and how it will intersect with the other parts of the system. You have to set testable standards, and then...y'know, abide by those standards.
Sometimes, this has knock-on consequences. Fireball isn't allowed to be stupidly more powerful than most other spells, for example, because when you have that kind of imbalance baked into the core, "power creep" becomes nearly unavoidable. After all, if nobody can say it's more powerful than fireball, surely it can't be overpowered! Right? ...right? Except that it totally can. If fireball is a huge outlier compared to other spells of its level...and new spells come out that are on a par with (but not better than) fireball, and you keep doing that once or twice per book...by the time a few years have passed, even with 5e's glacial release schedule, you've suddenly pushed out 90% of the spells from the PHB.
This is why I don't actually agree with Snarf's claim that unbalance in the core book has zero relation to power creep. IF it's the very specific situation given in the example--three classes that are pretty much even, one class seriously weak, and that class gets new additions that fix the gap--then yes, absolutely that's not a power creep thing. But we can use an example from another edition to show how unbalance in the core rules does in fact lead to power creep.
I give you the contrast of two 3.X feats: Toughness, and Natural Spell.
Toughness is a joke. It is a terrible feat. Absolute garbage. The only context in which it has any use at all is a convention game where you're not sure you're going to survive to 2nd level, so those extra HP might literally save your PC's life. Otherwise, you should avoid it like the plague unless it's a prerequisite for something else.
By comparison, Natural Spell is almost inarguably the second-strongest feat in the entire PHB; its effect is that the Druid who takes it can cast spells in wild shape form, which means, in general, it is acquired immediately at level 6, the first feat you get after gaining the wild shape feature. (The strongest is Leadership, since it effectively gives you a second slightly weaker character for the price of one single feat, but its strength was quickly understood and most DMs banned it for that reason.) Natural Spell is so powerful that, in 5e, which is inarguably extremely similar to 3e, the effect that Natural Spell grants is the 18th-level feature of the Druid class. And spellcasting in general was almost exclusively more powerful in 3.X than in 5e. That is how stupidly strong this feat is.
This design choice, to have such stupidly massive power disparity in the core rules, leads to three deleterious effects that hasten power creep substantially:
Bad feats, like Toughness and Mobility, will now be used as gatekeeping devices to slow the progression to really powerful later stuff--a choice that occurred rampantly across 3.X/PF. But then...you get ways to get these feats without spending your proper feats on them. Lots of ways, actually. There's an entire guidebook for it on GITP. So these "bad" feats become a gateway for power creep, by being used as "justification" for future great power...except that the stumblign block part theen gets removed, so you just have great power with effectively zero cost.
Amazing feats can still be written that are less powerful than Natural Spell....and more powerful than anything else anyone might be interested in taking. Because the ceiling is so damn high, there's almost no reason NOT to push things into the stratosphere. Sure, you aren't pushing the maximum/outlier points any higher, but you're absolutely shifting the center of the distribution higher and higher.
These pervasive issues propagate outward and upward, as if contaminating a food chain by poisoning the algae and plants. (As Snarf said, no analogy is perfect.) The vast majority of "Fighter bonus feats," for example, are closer to Toughness and Mobility than they are to Natural Spell, Leadership, or (to cite a PF example) Sacred Geometry.* But...with the Fighter class completely dependent on feats being good in order to be a good class...you can see how this disparity could lead to issues. If feats collectively cover a really really broad range of power, but important subsets of feats are clearly crap (examples already given) or clearly OP (e.g. metamagic feats), then it's extremely easy to fall into the trap of viewing the whole when you should be viewing the parts or vice versa. (Gotta love Simpson's "Paradox.")
These three get further compounded, then, by the fact that attempts to avoid power creep within one class can result in power creep between classes. If Fighter is underpowered, but you refuse to recognize that fact, then we get things like what Snarf said above WRT: Rogues and Steady Aim. If you're of the belief that the existing 5e Rogue was 100% fine, zero issues, then Steady Aim is necessarily power creep--you need to have TCoE to "keep up." Conversely, if you're of the opinion that Rogue was weak (which, I think, most fans did think that Rogue was weaker than most other 5e classes), then Steady Aim is simply bringing the straggler closer to par, which Snarf already said is a perfectly fine thing to do!
Point being: Significant imbalance in the core can absolutely encourage future power creep, doubly so if the designers fail to recognize or understand what the problems involved actually are, or if they cling to incorrect and deleterious beliefs about the systems in the game. This is one of the many, many reasons why it is so deeply important for game designers to actually define what their design goals are, set testable metrics for meeting those goals, continually evaluate how they're performing (and whether those goals were, in fact, actually wise in the first place), and iterate based on both testing and player feedback.
When we treat game design as a pure art, we encourage power creep. When we recognize that it contains both elements of an art AND elements of a science, we can significantly discourage power creep while still producing a rich, enjoyable game experience. Game design is necessarily teleological; I wish more designers, and more importantly more TTRPG aficionados, cared more about the ends of game design, rather than almost exclusively caring about the aesthetics of game design, the appearance of the rules.
*I actually ran a character that used Sacred Geometry. It was for an intentionally very high-power game. I swore to the DM that I would only use it for prepping my morning buff spells and for no other reason unless I actually crunched the numbers myself. She actually gave me permission to use a calculator for it...but only if I coded up that calculator myself. I got about a third of the way through doing so before the campaign folded. It's really surprising how much you can squeeze out of just knowing a few math tricks regarding primes, e.g. every prime except 2 and 3 is either one more or one less than a multiple of 6, so if you can generate 6, 1, and your multiplier, you're golden. That cuts down the search space IMMENSELY.