SenjutsuSage
Banned
All the Spirit Bomb did was recharge his energy.
Yep, the spirit bomb only gave him energy to stand and fight for a while. It isn't responsible for any of the power that Goku was displaying, and neither was it the reason for his appearance.
It served as a trigger that allowed Goku to tap into potential that was way down deep inside that he couldn't easily achieve on his own. Goku kept getting stronger and stronger through new super saiyan forms, or techniques like kaioken, but his normal, non super saiyan state hasn't been evolving to anywhere near the same degree as everything else.
Making the base form rise to a whole new plateau of power is the secret Goku has been missing all along. What we witnessed from Ultra Instinct Goku was his new max base of power. A new base that, through the strange heat, and perhaps the energy surrounding him, is very close to achieving a new kind of super saiyan or god state designed to allow him to take his new potential to an entirely different level. Even with Goku gaining the edge on Jiren further into their encounter, it was still clear to see that the further Goku went, Jiren too was able to follow. He still has much power he's holding back, or not fully revealing. Their rematch will be most interesting to say the least.