Why do you think marvel never upgrade his power & skill set?

@mrnihal: Because he is the only mutant who is closer to human. A human with a superpower is the same as having an extra part in his body. That is what happens with Summers. He has his optic blasts, which naturally comes off of its own and its function is to shoot anyone comes into contact with. Then there is the mystery surrounding his power's origins. At first everyone speculated that his body absorbs and metabolises ambient energy like his brothers and blasts them though his body. Then the question rises, if he can absorb energy like sunlight, electricity and radiation, why his energy never harmed anyone? For that, they came up with the explanation of his power being converted into harmless but powerful concussive energy. Then another question appear, if it so, then how does his body converts them and which part of it do so? As a solution, they completely changed its origin. The current version is that his powers are coming from a universe full of nothing but infinite source of concussive energy and his eyes acts as a portal for it.

Then there is the controlling part. At first people thought it was due to a physical concussion on the back of his head. But then it was speculated to be psychological. Then it was broken by the phoenix force. Each time he tries to gain control over his power, he gets great results, but in the end it was all but removed and his powers are broke once again. Because of this cycle, he always fears his powers going out of control, which is the same as human's fear of unknown. Finally his character journey where he started out as a troubled young teenage who wants to help his paraplegic mentor realise his dream of mutants and humans coexisting is a world by leading a team of young misfits with powers like his to play the role of superheroes to a ruthless cult leader who joins with a team his former rouges to protect and preserve his kind by any means necessary.

His character journey is one of the interesting and grounded journey when it comes to the X-Men. So giving him a new power means it has to grant him an ability which makes him both the top dog in the game but also reminds us that he is still human.