Velious doesn't have much in the way of undead for charming and leveling. The reason why HS is the best place a necro can level is that you learn all of the intangibles, not just charming: situational awareness, timing, patience, order of operations, and it builds intuition.
There is simply no better place for a necro to go to learn these things and due to the high level of risk involved, the experience sticks. One can always tell a necro who never leveled in HS versus one that has. Friends within the necro community tend to agree.
You can get great exp in KC on basement and make some money to boot at Verix camp. The best exp will come from root stacking the adds on top of your pet so the mobs kill your pet fast, break charm 4% and below and deflux for full xp gain, rinse and repeat.
At 57 you're too high for basement in HS and you should try North to begin learning all of the intangibles, then head to West for the best xp in the game, especially with a duo partner. Stay on the 1st half of the zone, the key that drops in the back room also has a charge of chloro and it respawns before chloro fades, ensuring a never ending free chloro. I'll put a video up soon of HS West.
Here's a video to help for KC basement, make sure you use DA after charming PH/Verix to turn mobs back to him, then just start rooting and get them stacked together as close as possible. Sometimes the mobs don't turn, just run towards your pet and they'll shift off you while harmshield is active.
https://youtu.be/5rJqawmJiYY
Unchained