Weak Constitution? I Instead Created The Mage System WCI

An accident caused Ron to be transmigrated to a world of swords and magic. There was no fancy magic here, only breathing techniques that had reached their peaks.
However, Ron was born with a weak constitution. His innate ability was considered low. He was told that he was useless and would be unable to practice cultivation his entire life. He could not accept this. He decided that he had to forge his own path.
As fate would have it, he discovered that there was a rainbow-colored crystal in his mind. Through meditation, he could sense free flowing multi-colored lights in the air around him.
The red light was scorching hot, the blue one was cool while the green one was refreshing and full of life. Ron was dumbfounded. What was this?
He subconsciously absorbed the light spots and moved them towards the tip of his fingers. A fireball appeared and burnt his door to a crisp.
From that day forth, there was a new job class on the continent known as the mage.
When some of Ron’s enemies saw him appear on the street with his weak constitution, they wanted to ambush him. Before they could approach him, they found themselves in hell.