I was doing some reading on Legion and when you factor in all the powers he has or could have and powers levels of those powers isn't he way more powerful then X-man/Cable?

Yeah, Nate has near unlimited telekinesis/telepathy, but if he got his mind under control Legion has the genetic potential for telekinesis, telepathy, pyrokinesis, teleportation, time jumping, shapeshifting, prehensile tongue, ferrokinesis, atmokinesis, and manipulation of both molecules and radiation.  And he's no slouch in any of these powers as far as power level goes. 

So even if he can't actively access these powers all the time, the genetic potential is still there...so why isn't Apocalypse (or Mr. Sinister or Dark Beast for that matter) going gaga over him?  I mean in all honesty hes spent most of his adult life in a catatonic or comatose state so its not like he'd put up a fight...much.

So much for the potency of the Summer and Grey lines.  Apparently all you need is a shady old psychic and a brassy jewess who smokes too much and you get an Omega Mutant :)

Because Apocalypse is smart enough to not mess with someone who "seduced"  his own mom. 

Being the son of the almighty Cyclops & Jean Grey was a bigger deal in the 90's than being the son of Xavier. 

When Apocalypse was a major villain, Legion was still inexperienced with his powers.  Even then he only had access to telepathy, telekinesis & pyrokinesis. 

Meanwhile, back then baby Nathan Christopher Summers was the Harry Potter of his time; destined to kill the villain Volde-lypse.  Therefore the villain sought to destroy the child before he could be destroyed by him...

Actually I think it is due to the Phoenix Force (Jean Grey/ Madelyne Pryor) where as Charles Xavier doesn't have that in his bloodline.

The reason Apocalypse has such a boner for X-Man/Cable is because he asked Sinister to create for him a form that would be omnipotent, a shell he could wear that would never die and would be all powerful. Sinister engineered X-Man/Cable as he was asked, but not for those reasons. Sinister saw Apocalypse as the ultimate danger to seeing his life's work final out and so he made a being that was everything Apoc wanted but to destroy him. not become him. Legion, while badass powerful, is too unstable and too much of a challenge to control to get to the point where Apoc and Sinister could do anything with him. Plus, Legion's mom is human, big no-no if you are a mutant tyrant who promotes humans as inferior and mutants as deserving survival of the fittest. Makes you look just a wee bit hypocritical to your underlings.

Why not go after Scarlet Witch?  Granted That even with the House of M event that her power to take away mutant powers indefinitely came into question with the arrival of Hope but the same thing can be applied to Legion.  He's the only one to actually give a mutant back his powers with out plot technology like Magneto.

or how about Franklin Richards, Rachel Summers, or Vulcan (before he died)

Basically any omega level mutant (Jean Grey, Nate Grey (Before he lost his powers), Hope Summers, Iceman, Mister M, Quentin Quire, Elixir, and Legion)

I would like to see him use iceman. I would just like to see Iceman be part of something larger and seeing his abilities put to good use (Story wise)