No no no... this is PRE-Crisis Supes, ppl. PRE. You're thinking too much along the lines of the current weedy little 'I get hurt by really powerful punches' Supes, rather than the 'I'm invulnerable to everything except K-Nite and Magic' Supes.
And no, PreC Supes was immensely resistant to telepathy. Telepathic villains were regularly astounded at how easily he shook off any probe into his mind.
You forget - Superman was SUPERman. He was designed to be invincible. You take Supes from the fifties and you can tell him not to use his hands or feet and he would STILL whupp Onslaught.
He would vibrate so fast that he becomes invisible. Then he'd fly faster than light around Onslaught to create a vortex, then lob a coupla dozen planets into the vortex to keep Onslaught company.
It'd be like watching a Frog in a blender.
Or if Supes was feeling REALLY cruel, he could sneeze....
He literally destroyed a star system - planets and all - with one sneeze...
And people call POST-Crisis Supes overpowered, lol?
Ok...let's say telepathy is out as a means for killing Supes (something I still wouldn't completely concede, since Onalught is a much stronger telepath than any Pre or Post Crisis Supes has ever faced...Manhunter included).
But for the sake of debating, how about hordes of metal swarming at Supes at ridiculous speeds...he's as durable as steel, right? So steel and other forms of metal would hurt him. All this, while the telepathy at least bothers him enough to be sufficiently distracted for Onslaught to get some blows in.
Still stickin' with Onslaught.
-DM
You also forget that oslaught has astral projection,pisonic blast (that can go through invulnerability), mind bolts blast,he has the combine powers and intellagence of xaiver and magneto and he can manipuate fields natural and artficial.Onslaught powers alone are godlike longer the fight last more of chance of superman getting killed or being a puppet of onslaught.
No, Supes is not as durable as steel. Just because he's called The Man of Steel doesn't mean that. It says Hovis on the side of Buses, it doesn't mean they sell bread.
And, okay - I'll concede that Onslaught may be more powerful with his mind control techniques than anyone Supes has had to handle, which would prob mean he'd lose.
But again, this is PRE Crisis Supes. Think of the possibilities dudes, lol. That's the reason for pre-crisis Supes - he can do anything, which gives the writers great licence for making him do ridiculous things, lol!
He moves far faster than the speed of light, so no energy blast of any sort will get near him if he doesn't want it.
Plus, like I said - he can vibrate his molecules and make himself intangible. Maybe that would stop Onslaught's mind control? Failing that, once Supes found out about Onslaughts monster telepath powers, he could go back in time with this new info and just throw planets at the guy before he came into range, or get Bats to make him a telepathy reisistant helmet lol.
In fact, PreCrisis was a super-genius as well - he could make one himself!
The list goes on, which is why the CoIE series happened.
Onslaught becuase at full power he is technically much more poweful than any non comsic entity and most cosmic entities beacuase he is always evolving into something better. Thus it is in his reaches to become omnipotent. Even Onslaught at his height as seen in the comics would thrash Supes precrisis and Onslaught at his actual peak would beat Superman Prime.
Onslaught easily.
Full powered Onslaught had the combined powers of Xavier, Magneto, Franklin Richards, and X-man (Nate Grey). Pre-Crisis Supes was ridiculously powerful, but against a being that can warp reality at will and destroy his mind, not to mention attack his polarity and molecular cohesion through magnetic and telekinetic manipulation, Supes is just out classed, even Pre-Crisis. Onslaught created a sun to destroy New York City with a thought. With Franklin's powers alone Pre-Crisis Supes is outclassed. Onslaught could make Supes powerless through Franklin's reality altering abilities, then torture him with psychic images until he begged for death.