Do level 5 units rule this game?

[Metathron]

In the last two games I played, I used units level 4 and below up till the moment when I found level 5 units, at which point I summarily ditched lower level units and played with just the level 5s. I started a new impossible paladin game last night and I'm thinking I could force myself to try out some other lower-level unit combos, but the temptation of using level 5s again might prove too great.

So my question is, are most level 5 units in KB:AP just a tad too good? Or is the balance just right in your opinion?

I think the archdemon, at least, might be overpowered at 1600 leadership and a measly 6000 gold (IIRC).