Well, we know that Servants vary in strength greatly. Assuming that the only difference betweeb normal Servant and Grand Servant is a scale, we must conclude that some Grand Servants should boast power on the level of several Grand Servants. Also, Primare Murder +Altroughde is most likely stronger than Crimson Moon an Altrouge is probably on the level of regular Servant.
The falling moon is an application of his Reality Marble. Unless he can't make his RM expand on another planet, then sure.
Many things could have happened and not all of them points to them being defeated. Because Ado Edem is good at killing large enemies, he didn't stand out in the battle against A-Rays. Black Barrel sure didn't do anything to Type Saturn, as did every other being on the planet at the time sans Ado Edem.
The priest was waiting for the arrival of the princess, who was only an enemy of all of them.
For the priest, the golden princess was the one and only main heroine.
Everyone else was unworthy of his respect, no matter how strong they were.
Tsukihime 2 Prelude III
Then it is possible to argue that we have no confirmation that mirror imafe of the moon is full equivalent of an actual moon.
Also, just because one Type could have copied his celestial body does not mean that others can. They just belong in the same group, that does not mean that they all have similiar abilities, or that they are even on the same scale power-wise.