I'm sure many will disagree with your ranking. Personally, I completely disagree with the placement of the Succubus and Archdevil. The Succubus is highly situational and can lose to any level 4 unit (although it can also win, but I would put it in 4th or 5th place). As for the Archdevil, it only wins against the Ghost Dragon (although in a 2 vs. 3 battle, the victory will be with the dragons due to the curse), because level 7 is very balanced.
In my opinion, in a game with Inferno, the main thing is to accumulate Imps and consume (preferably completely) the enemy's mana, and then Dark Magic, good initiative, and attack will do the rest. If this fails, there may be problems. But the Castle is still interesting.