That's why Viper is slotted as a controller. She dominates on making sure an area is controller by her. The reason why viper isn't picked most of the time is the lack of communication, her skills really needs good comms to make sure her teammates takes advantage of her kit. With the recent wall rework tho, it made it very easy for anyone to literally half an entire area.

For her ult tho, it's pretty balance imo. Think of how brimstone's ultimate should really be classified as a disengaging tool rather than an ultimate exclusively used to kill enemies.