Understanding
The fusion technique was definitely the best that the Zone had and Leonel had spent enough Demon Points to make certain that this would be the case. However, even it required at least a basic affinity already existing for the fusion to be perfect.
Luckily, Leonel's Dream Force affinity was as high as could be and he had more than enough Spatial Force affinity thanks to his Ethereal Star Force. This met the basic requirements necessary for the fusion process.
Once the fusion was completed and perfect, nothing else would matter. After all, by then, the base of Leonel's Spatial Force affinity would thus become his new Innate Node. Whether or not he kept his Ethereal Star Force would become irrelevant by that point.
In addition, due to the fact his innate Dream Force affinity was so high, the Emulation Spatial Force Innate Node would be even more powerful in his hands.