...How in the hell can you lose with all those dragons on your side.
Inverse ninja law. Having all those dragons, makes them much more likely to lose than summoning just one dragon.
Possible outcomes:
1) Self-replicating low-level spells annihilate dragons.
2) Level 3 spells custom-tailored to slay those specific dragons.
3) Meta spells interrupting the summoning.
4) Spells redirecting dragon breaths towards other dragons, making them kill each other.
5) Summons mice. Dragons are afraid of mice for no apparent reason.
6) Spells outside of level system. Ancient sorcery technically isn't spells higher than level 3. Just like it's not technically forbidden to summon godlike dragons.