Yes, that's true, but Dryads have more initiative and can hold back the Imps with their swarm, while the rest of the army can approach the enemies... and if you create a Phantom too! And what are Archers for? To kill Imps! :D
You can also create a Phantom for the Imps))) And it steals mana just as well as the original))) Besides, Imps move before any Archers... and then you can just kill them - they've already done their job)))
Imps are definitely more useful... not only do they steal, but they also pass everything on to their owner)))