Cable was stated to be a multiversal nexus of time and space so his full potential being universe level isnt that farfetched.
This is not a case of "a human is not multiversal just because he creates universes with his decisions" but this is not the case as Cable was explicitly stated to be nexus of time and space.
Well, it would be made up based on that as being a "nexus" is meaningless. It could mean
anything, maybe (and probably) time and space need someone to do certain important actions in their life to keep their own balance, meaning that Cable has no extra power nor new weird abilities due to being a "nexus", and this is simply a weird mechanic time and space are being stated to have. As in, if I grab a regular cup and say that it's the nexus of the concept of cups, and if it gets destroyed the concept of cups gets destroyed, but then if it's a regular cup, then it is simply a regular cup and the thing to make out of this example is that the concept of cups has this very weird self-destructive mechanic that characters need to take care of by looking over that cup.
Or maybe Cable's case is somewhat different, and the classification of being the "nexus of time and space" also grants him
something supernatural (that isn't sheer power) that only he has and that time and space react to in a way that balances them.
I would be saying the same outside of Marvel, which in particular loves to apply nonsensical rules like that that nobody follows later (
Cosmic Ghost Rider Destroys Marvel History parodies this near the end, making up rules & classifications similar to what Cable has going on here, though completely ignore this last bit if we're still going to talk about the nexus thing).
Even if its not by purpose Cable already has shown to have multiversal Influence due to him being a Nexus.
That's not true due to not being proven.
Also, Alecto scrambled the mind of Irene so that Cable won't be able to read it and Cable broke pass that defense set by Alecto when he was Savior.
"Scrambled the mind of character so that a telepath won't be able to read it" sounds like it's making the job more difficult, not impossible, since something scrambled can be ordered or be seen as to how it would be if ordered. If it took him time then it's even less notable.
He also easily breached Deadpool's (who was infamously "immune to telepathy" which even Prof X, Onslaught and Jean cant breach ) and Silver Surfers psychic defenses with his last bit of power.
That is notable.
He also easily destroyed Silver Surfers board, which contrary to what people think is not an easy feat that anyone can just do. The Hulk and Ravenous were unable to even dent it when they tried to break it. Cable vaporized it with a single attack.
The Enslaver( Mrrungo-Mu) (Silver Surfer: The Enslavers #1), Durok (Thor #191), Aegis and Tenebrous (Annihilation#1),Molecule Man, Morg with Power Cosmic + Waters of Life and the Stranger are the only ones shown to have similar feats and they were not enemies that SS can just beat half assedly (All of these characters were shown to be superior to SS in a fight and were only defeated using some sort of weakness/bfr)
Nathan as a baby also granted Apocalypse (3-C) enough power to be able to shrug Black Bolt's(3-C) full power scream. He later gave Cyclops a boost in power which enabled him to one shot the boosted Apocalypse with his blast.
I'm ok with all that.
