Atlan didn't know that there was such a rule in missions. But if that was true, then he understood why they limited the amount of Saviors in this mission.
If the City dispatched 50 Specialist-level Canzers, then that would mean that the Remedium could also have 50 Specialist-level Canzers waiting for them inside. No matter how strong humans were, they could not hold a candle against a Canzer's ability to regenerate or make clones of itself.
Yes, with 50 Saviors all working together to fight the Canzers, they might be able to subdue them for a long time. But, things could always go wrong. There could be an anomaly amongst the Canzers that the Operators had not prepared for.
It would be troublesome enough just to carry 50 constructs inside. Logistics alone would mean that at least half of the 50 Specialist Saviors needed to carry the constructs inside the Remedium. After all, they had no other Porters left in the City other than Atlan.