Just feels like him ignoring the pieces he has, trying to do something with them (infuse dragon energy), if not just risking using them is kinda plot forced to drag it along. He literally: oh cool, I got this.... and then forgot they are there when he showed no issues with changing if needed, for power.
The mc's power is regrettable. He activated his sacred mechanism years ago and he barely has the energy level of a low class. That's garbage. Totally stupid. The truth is he should be stronger, much stronger, and that's not to mention that even a secondary character has more than him eating yanagi and not even training is total garbage