Imagine the AAA+ RPG game you've been looking forward to for a long time has finally been released after years of development. You spend an hour downloading it with stars in your eyes, already anticipating this game you've waited for so long. You grab a beer, get some snacks and the moment the game starts... your character is already fully maxed out.
First off, boredom is a feeling, as such it is subjective. You may find OP MC's boring, but you cannot say "MCs OP from the start are boring", because everyone has different ideas on what is boring/interesting.
That's the same feeling I have when I enjoy reading the first chapters of a novel but the MC suddenly gets overpowered for no apparent or logical reason.
Can't the lack of reason be interesting in itself? I can totally imagine a great story where the MC is suddenly given god-like powers one morning, and he has no idea why. How will the Mc react? What should he do with these powers? Was he given them for a reason? Where do they come from? Go on a jouney of self discovery and travel the universe in an attempt to find these answers! And if in the end it was just a random fluke, he did nothing to deserve it, that in itself can be a commentary for the worldview that the current power of humanity being the result of an evolution fluke.
Of course I can see that a lot of novels don't do that, and the OP mc is simply going to mindlessly rampage his way through the world, but that is an indictment on the poor quality of these specific novels, not on the concept as a whole.
I'm not saying it's bad for the MC to have some powerful abilities or skills, but it's just boring as f when he got them from the start with no effort. Mainstream JP isekais are masters in this, sending depressive salary men or retarded high schoolers into another world and yet they somehow end up lv999 or they get op sht from a bitch who call herself a goddess. This generic recipe ruins the plot imo.
It would depend what plot. If my plot is that my mc is suddenly burdened with more power than he knows what to do with, and has to deal with the moral implications/consequences of said powers, it won't be an issue. (this is the plot of a lot of superhero movies, where the MC is the only one with powers, completely OP, but being powerful does not mean not having no problems.)
If the plot is the mc winning a competition of pure strength, then giving the mc having overwhelming strength would hurt it.
I might not be a big fan of Chinese cultivation novels, but at least their protagonists still have a learning process and they often go from weak to strong even if they have some kind of special powers like a grandpa stuck inside a ring or the soul of the Heavenly Demon Of My Ass. Same for Korean returner/ranker type of novels. I know I'm just venting, but I find the slow-progress type of stories much more interesting tbh. No matter the genre, be it a fantasy, sci-fi, or realistic novel.
So you like progression stories, that's fine. It's personal taste, and you liking some types of stories more than others is perfectly normal. That doesn't mean that the genre you dislike is worse.
In my own novel, I definitely crippled my MC during his first fight and I killed the entire human race + most of the few survivors in the first narrative arc. I know I'm not a good example to follow as I basically set up the difficulty at Hell-mode from the start lmao ; but at least it gave my MC a goal to reach, and a reason to move forward.
I generally dislike novels where the MC is weak. I prefer rambo characters that have the strength to do something about what they see in the wrong world, instead of desperately struggling to survive. My opinion doesn't make underdog stories any worse, it's just a matter of personal taste.
To take the previous comparison, it's kinda the same reasoning as why you would want to slowly improve your character through a rewarding process in a game (for an RPG it would be quests, drops, exp, etc.), instead of already starting with a maxed-out character that can os all the mobs with no effort.
But there are plenty of games where you start out maxed out. In games like subnautica, poly bridge, soma, speedrunners or slime rancher, your character never gets stronger. That is not because they are worse than other games, they have simply decided to focus on other aspects of gameplay/story.
IN Titanfall (an FPS game), you don't level up, and are much stronger than the average enemy. You are OP, and they only win by numbers, but the story and gameplay are still top notch.
In planet coasters you can build city-sized roller coasters and send people flying to the moon with a well aimed crash. Minecraft has a creative mode where you can build/destroy anything, and many players love to craft beautiful worlds with it.
You cannot criticize a story for having an OP mc. You can criticize it for resolving all its issues too easily, undermining its stakes or having no tension, but that can happen whether or not the MC is OP.
Sure, most stories with an OP protagonist are badly written, but then again most stories are badly written. There are plenty of good ones out there, like Re:write, Song of Void, One Punch Man or Overlord.
Even then you might find these stories boring, because personal taste is subjective, but that doesn't change the objective quality of these novels.