Yes, there are strong units at many levels.
However, first of all, not at all levels, and secondly, regarding "head and shoulders above" - that's an exaggeration.
Halberdiers are certainly "beefy," a good unit, but their speed is not very good.
Archers are good, but only upgraded ones.
Griffins are also good, no argument there, as are Crusaders, but saying these three units are unequivocally the strongest at their respective levels is an exaggeration.
Monks are frankly weak, let's be honest.
The power of Cavalry heavily depends on the "cavalry bonus," and in any case, Naga Queens and Death Knights are at least no worse.
Angels are strong, no questions there. Although the computer considers Devils to be stronger. No Retaliation is no joke.
Well, as for Archangels - yes, they are the strongest. Though even here it should be noted that there are units which can successfully resist them.
Overall, Castle is good, but not so much that the others have no chance.