As for djinns, if they weren't large creatures, they would have a better chance of survival. But as it is, they are fragile creatures, and I usually hire them last, considering the fact that 122,300 is spent on purchasing non-elite creatures in the Academy (3rd most expensive after Sylvan and Inferno).
Liches are versatile – they are both archers and spellcasters (their magic is the best among all spellcasters).
Undoubtedly, liches are traditionally essential for Necropolis as good archers with their cloud attack. But I don't think they are the best creatures of level 5. In my opinion, nightmares and unicorns are much better.