Post-match analysis.

Thank you for the answers!

And what is the minimum native army for the Swamp faction needed to be able to capture the maximum-level Conservatory (5 stacks of 40 Griffons each) so that the exchange is equal (if possible, with a description of the battle turn by turn)?

Hydras in the castle with a full purchase + a well-leveled Titan (level 6-8 with experience armor), haste, and bless in the spellbook. The task is to gather 3 rightmost stacks into one pile and use the hydras with bless to attack them all at once, in the 2nd round, use haste and attack all three again; few will remain. The remaining army deals with the left flank.

All hydras and part of the vipers should survive, the rest is lost; 4 angels will more than compensate. Take only single units of flies, don't take bulls at all. It is desirable to upgrade lizards and gnolls to match the speed of the griffons.

Maybe not the minimum, but something like that.

All of the above is for a battle on swamp terrain.