First of all, it's not stupid-not stupid, but the question is whether there is money for it. If there is money, then it's very much not stupid.

Secondly, sorry, but don't talk nonsense, 2-3 angels cost 6-9 thousand, that whole mishmash of horses, marksmen, crusaders, pokemons costs about the same, and even considering the cost of building upgrades, much more, plus building time and the hassle of moving troops for upgrades. A hero with angels runs around doing his own business at maximum speed and doesn't bother. Fact ;)

Here's where the interesting part begins, the second option of course rules when breaking through walking fat monsters like golem hoards, but it methodically melts against shooters and when taking serious objects (Dragon Fly Hive for sure, Griffin Conservatories are no small fry if without Mass Slow either) and generally against more or less serious monsters, and so on and so forth, there are plenty of examples. Angels, when handled skillfully, have a strange habit of staying alive, albeit with a few hitpoints at the end of the battle ;) . Fact.
Furthermore, almost always there are at least a couple of conservatories on the developed territory, and there is a good chance to form a strike stack of angels, for example, 5 angels are an order of magnitude more effective than 3, and later on in Dragon Utopias, the more angels there are, the less chance that the dragons will target them instead of the [neutral] feeder. Fact. This is more than compensated by the attack, defense, and speed, as well as the health of angels, as I already said, with skillful handling, angels usually survive where the second option loses out, slightly, but still loses.
Conclusion — if there is money, you can build angels in the fort without a second thought, and if the castle [resource income] is building up, it's simply perfect. Try to refute that ;)