Regular readers will be well aware of how dull I find the concept of "the most powerful" superhero that the internet is somehow still fixated on. Mathing out how strong a character "really" is has no appeal to me, as I tend to enjoy narratives for being, you know, narrative, and not an exercise in statistics. That said, when people pull out the whole "well this character is strongest because X" nonsense, I do like to have something in my back pocket to shut the argument down and move on. Golden Age Superman, Stardust the Super Wizard and Doctor Manhattan are kind of your 'ad absurdam' responses there, by the way.
That said, I have thought about this at least a little, and come up with a list myself for this 'discussion' when it raises its ugly head. Naturally, I dug pretty deep and came up with some strange and niche characters because, well, that's kind of my thing, isn't it? So strap yourself in for a list of crazy characters that break narrative fiction with their outlandish powers and put any of your Gokus or Supermans Primes to shame.
Sun Wu Kong
Look, why bother with any Shonen anime protagonist, when you can just have the character they're all riffing on? Sure Goku or JoJo can teleport or run really fast, but can they jump the entire length of the universe from a standing start? Undefeated in battle, outsmarted only by the Buddha himself and so strong he can lift heaven, Sun Wu Kong, the Handsome Monkey King, puts almost every modern superhero to shame.
Fantomah
C'mon, you knew Fletcher Hanks was going to show up on this list somewhere and Stardust is really more of a villain by my standards, so that left Fantomah, Mystery Woman of the Jungle. Fantomah's powers are difficult to truly quantify as she, like many Golden Age Ubermench, can basically do anything at any time with no real justification needed. Able to fly, turn invisible, become intangible and transmute basically anything, Fantomah uses her godlike powers to inflict ironic punishments upon those who violate 'jungle law'. No returning antagonists for this superwoman, the first super-powered female in comics history, they're all dead.
Golden Bat
Indigo
The superhero from Robert Mayer's classic pastiche novel Super Folks, imagine an aging superman who's powers have slowly been draining away until he realises that the entire city of New York is laced with his one weakness, Cronkite. Once freed from this influence, Indigo is once again capable of astounding feats, literally punching the antagonist of the story out of the universe. Indigo is very Bronze Age comics in his presentation, but has retained all the absurd powers that symbolise the Golden Age, think post-Death of the Staceys Spider-Man in terms of neuroses with the powers of Doctor Manhattan. If you're a comics fan and you haven't read Super Folks, you really should check it out.
Tesseract
You want deep cuts? I got deep cuts. Tesseract is the greatest warrior of Halcyon, also known as The Everywhere Man and the Totality Warrior. The unique power granted to Tesseract by his magic tree mommy is that every version of him across the multiverse is connected and fight in unison. Man, Ultimate Fantastic Four was a trip. Seriously, when this guy punches you, it's actually an infinite number of him punching you, that's crazy. This guy is so obscure that it's genuinely hard to find much information on him, especially as the Cosmic Cube stole his name for the MCU, but if you have a chance to read some Ultimate Fantastic Four, try it out, it's not really good, per se, but it is very interesting.