Unown E is not broken, none of the Unowns are... some are quite bad actually.
Unown E may seem good, but it really can hurt you as much as it can possibly benefit you. What if you don't know what's in your opponent's hand? You could be using Unown E to simply HELP your opponent evolve faster. There is no choice in which basic to bring down if your opponent only has 1 in their hand, you could technically help them win the game because of that extra turn. You could also look at your opponent's hand and find nothing there at all, a simple waste of an attack which you opponent can use to his or her advantage. In the end, Unown E seems to disadvantage you more than advantage due to the randomness (unless you know what's in your opponent's hand), however that depends solely on your deck's strategy and if you're able to complete any specific combo to benefit from Unown E's Hidden Power at all...