Kurosaki Ichigo was simply born to cultivate the Bleach system!
But rather than cultivation, it was more accurate to say that, like Zaraki Kenpachi, he constantly adapted in battle and unleashed the power that had been suppressed within him.
That seemingly cheat-like cultivation speed from before was still the result of the powers within him restraining one another. For instance, his Quincy power—the Yhwach from a thousand years ago—had always been suppressing Ichigo's true Bleach power.
Meanwhile, Ichigo himself feared the power of the Hollow, so he could not use it fully at all. It could only serve as a temporary cheat.
When he first awakened his Zanpakuto, the reason Kurosaki Ichigo seemed so weak, like a newly born Bleach, was purely because he lacked a suitable method to draw out that power.
In the following events, in order to defeat increasingly powerful enemies, he learned Shikai with the help of Urahara Kisuke, the shop owner, and came to know his Zanpakuto's true name.
After arriving in Soul Society, he learned Bankai within three days, achieving something ordinary Bleaches would struggle to accomplish even after hundreds of years. Within a month, he had basically mastered the use of Hollow power and condensed it into a Mask.
Throughout this process, Kurosaki Ichigo had merely used proper methods to guide out the power already within him.
Even by the end, the true upper limit of his power had never been fully revealed.
A guy like that was going to pass up the Bleach system to buy a Kryptonian Bloodline and coast through life?
Wouldn't that be far too wasteful?
Substitute Soul Reaper: "I was just saying. Even if I wanted to buy it, I don't have that many Points."
Kurosaki Ichigo did not have any direct understanding of his own potential.
Even