Izanagi literally spawned all three deities upon washing himself, though he would later step down from his position of power and give it to his daughter Amaterasu, and she is almost universally considered more important and powerful than her sole creator parent.
I have heard that his gift to her upon her ascension into rulership, the Mikuratanano-no-kami (A necklace of 500 jewels) is a symbol of his power, meaning that she inherited all of his power, though couldn't find any evidence of this.
See, the Kami have this thing where the most innocuous daily acts can spawn new deities. A Kami might be making a salad and cut his finger with a knife, and from his blood a deity can be born, or they can be born from lost limbs, from their spit, or imagination, or from their dying bodies. It is said that there are "8 Million Kami", though that is a more symbolical number. Instead, a more reasonable assumption is that there are an infinite number of Shinto deities / spirits, and this weird "Reproduction Method" of the Kami is partially the reason for their innumerable quantity.
However, progeny and age are not always an indication of a deity's power and authority over another, even if said deity was spontaneously generated fully-grown from a sole parent. In fact, this is the reason why Amaterasu is ranked as "Possibly Low 2-C" in her profile.
During the Edo / Tokugawa Period, Japan came into contact with European Christianity, and some of their foreign ideals leaked into Japan's local culture. This is notable in how many Shinto Priests started gravitating towards the figure of Amenominakanushi no Kami, who is the primordial deity of Japanese Mythology, and arguably the creator of the Universe, though his role and influence in the texts is minimal.
Regardless, he fit perfectly with the Christian concept of a Creator God, and many began looking at him as the most important Shinto God, even if he clearly isn't when looking at the texts. Other, more traditional priests disliked this notion, and their response was at times... Aggressive:
"The real intent lying behind the [Watarai's] preference for Amenominakanushi among all the kami is to insinuate that since this kami came into being first of all at the beginning of heaven and earth, his status as First Ancestor of Amaterasu-Omikami makes him superior in esteem to all other kami. But this is the most clumsy, pedestrian sort of reasoning produced by later ages, since there is no particular reason to think that coming into being earlier indicates superiority, nor that coming into being later indicates inferiority. If it were so, wouldn't it be true that all the deities that came into being before Amaterasu-Omikami were superior to her?"
So while Izanagi is a very important deity in Shinto, and the direct creator of Amaterasu, we cannot use progeny as a feat due to the nature of the Kami. However, I would indeed believe that he can be scaled from Tsukuyomi who is evidently Moon Level.