It's all very simple. All Inferno creatures have quite decent speed, which, when combined with acceleration, will allow them to reach the enemy. The Maggog and Cerberus ability will prevent the enemy from effectively protecting their archers! Demons, resurrected by Fiends, can serve as ideal fodder to absorb enemy attacks. Attacking Efreet is generally not a good idea. With large armies, you can already take significant damage from their Fire Shield, not to mention their attack! The downside is the lack of archers, except for Maggog, but two creatures don't counterattack, which is definitely a strength! And archers aren't always good; they don't provide retaliation, but they have a penalty in melee combat. In Inferno, only Maggog has this penalty. Cerberus and Devils can perfectly fulfill the role of archers without fear of a penalty. So, on a level playing field, is Inferno weak?
Of course, it's not very convenient for a castle siege, as only two types of creatures can pass through, but what types! The 6th and 7th tiers! We quickly eliminate the enemy's archers, forcing them out from behind the castle walls, and then overwhelm them with Cerberus and Devils. And Efreet, if we manage to lure them back out from behind the enemy's walls. The enemy will come out because, although Maggog are weak, there are many of them. If the enemy doesn't come out, we wait for the catapult to break down the gates, then quickly send in Cerberus and Devils to attack without retaliation, and finish them off with Fiends and Demons. If it doesn't work, it means the enemy played better and is superior in skills or spells.