Leonel knew what he was missing, and that was Dream Runes.
The reason he had been able to make the horned dragon so powerful was precisely because he had so many formed Runes for his Scarlet Star Force Stars. Leonel knew that if he wanted the strength and stamina necessary to succeed in his plan, he would need more Dream Force than he currently had, and much more powerful Dream Force at that.
Under normal circumstances there was nothing that he could do about this. After all, though his mind was technically in the Seventh Dimension thanks to his Starry Tailed Fox Lineage Factor, it was shackled by his mind to too great of an extent.
If he wanted to mitigate this weakness, he could rely on his body. It was too weak of a vessel.