As a healer I honestly don't think DHs that that much of an outlier. Burst overall across all classes is absolutely too high, but DHs specifically are getting a bit too much attention. Yes they end up n1 on damage done, but most of that is aoe padding with fel rush and blade dance. Yes if they get close to you in meta they can melt away your health bar. However outside of fel rush, they are really not that mobile. It's much easier for me to kite DHs than it is to kite monks and rogues for example. Generally they are very easy to shut down. Interrupt their eye beam and CC them when they meta.
DHs are punishing for people that don't understand the class, or are not paying attention and cluster together while the DH is blowing all their aoe burst. If you stand in their artifact skill, of course you will die.
The one thing that is overtuned about DHs imo is throw glaive. When they cut DH mastery in half, they also buffed haste and crit by 25% which made glaive throw scale a bit too well.