I agree with you, but it has no chance of killing it, while Cerberus has a chance, it will keep dividing and overwhelm it.
If Manda 2 is going to restrain it then it will be busy with the dog, who will protect Kabuto from the other summons and paths?
I get what Your Saying, In the Long run Cerberus > Manda II.
But i think Manda Two could Handle Cerberus and Pains Other summons Going by the Sheer Size of Him, obviously After A long FIght he would get over overwhelmed by Cerberus while the Other Summons would of Likely have been Taken out by then. Thats it Manda II Doesn't just Go for the Paths and Kabuto Dealing With the Summons Via Genjutsu
If you Remember the Size of the Original Manda and His Size Dwarfs Most Summons and he is Even Bigger than Jman and Tsunade's Summons Due to his Length.
Also I think it's Unclear if Manda II us poisonous or Not, If he has paralyzing then Cerberus is Done for.
Though it is only a speculation at this Point in time.