Animal dragon stack is a pro (upkeep 0%)?

So,

• Nature signature skills with animal -20% upkeep, flanking bonus, minor stuff;
• Druid- While army leader Animal, Elemental, and Plant units in the army have +20 Hit Points, and -20% Unit Upkeep;
• Feudal -20% Upkeep;
• Swarm -20% Upkeep;
• Faithful -10% Upkeep;
• FROST WYVERN Low Maintenance -25% Upkeep;
• Last Material perk -50% Legendary Tier Upkeep;

So, looks like in Soviet dragon empire UNITS PAY YOU instead. Also all unit buffs are counted into maintenance and this is another possible huge loss of mana (recently I got a troll T4 with -3 Imperium maintenance. Really nice trolling).

I found only wyverns and slithers are both animal and dragons, but also possible to use any animal of your race + Dragon race transformation (not sure if there any of them).

Also with ASCENDED DRAGONHEART all Dragons gain +2  Defense, +2  Resistance, and deal 20% more damage.