We all know that web novels, light novels, and LitRPGs are absolutely saturated with overpowered protagonists. Sometimes they start out weak, then become OP by the the end of the first chapter. Occasionally, it'll take a handful of chapters before the protag gets crazy strong.
Or my least favourite: When a protag starts out weak with humble origins, but it's revealed that wow, they're not
nobody their parents were actually super duper special and
oh wow they inherited that too. Why does a peasant have to have a secret noble lineage to be strong?
Personally, I love it when an MC starts out weak (pathetic even), but through their own efforts (and with some help) they're able to become stronger. Not the strongest (at least not early on).
A series that does it really well is
Grimgar of Fantasy and Ash, the MC has a steady upwards trajectory (with a few significant setbacks), but it takes a long long time for them to even be considered notable among adventurers. The gap between them and the top parties is vast, but they still manage to be amazing and competent. It's a great balance.
How do ya'll prefer to write your MCs? OP from the get go? Weak, but quickly becomes OP? And how fast should it happen?
Personally, I'd say it all comes down to the execution and the focus of the narrative itself.
For some, it's completely fine for the protagonist to be overpowered, because of the inherent nature of the story's conflicts.
For example: Superman.
He's OP as hell, but it works fine for his story, because it isn't about whether he's strong enough, or powerful enough, but rather it is about the morality and ethics of his character. The question is never about whether he is strong enough to do whatever bullshit he is able to pull out of his ass to win the day in the end, and it isn't about whether he can grow stronger or not.
His story's conflicts are often about morality, and "Doing the right thing" which lets him be "as strong as he needs to be" without derailing the story.
When the series does feature questions, or concerns, about growing stronger (leveling up, or what have you), then there should definitely be a steady upward trajectory built into the narrative. The biggest issue with this that I've seen though, is "power-creep" since the threats the characters face also need to continue getting "stronger" as well to maintain the dramatic tension and sense of danger. Keep it up and you'll eventually end up with powers and abilities in the absurd ranges if you're not careful about your execution. Which really doesn't translate much into enjoyment (for me anyway). I much prefer when the characters start off "weaker" and have to "work at it" to gain anything substantial, yet those 'substantial' gains are never elevated to the absurd degree that some (most) shounen series tend to reach.
As for what I prefer for a main character(s), honestly, a mix of both, and there is one motto that I live by with regard to all of my own writing projects, as well as what I tend to look for in the fiction I'm reading, as far as what the characters in the story are capable of.
Special, but not Unique.
There is something that makes each, individual, character special in the story, but no single character is "unique" in this regard. There is no single character who can achieve everything they want to, without cost or effort, and most often, they need to work together in order to achieve their goals.
I build this into every TTRPG campaign I've run over the last twenty years, and the same holds true for the fiction that I write (and personally, the fiction that I enjoy the most).
When the characters are all distinct, and contribute meaningfully to the story and the plot (in their own way), then I tend to find a lot more enjoyment when I'm reading, or watching. For example; The X-Men; Fate/, etc etc.