Blizzard has tried to balanced them before. In BfA they added Animal Companion but it preformed underwhelming. Players were disappointed and Blizzard tried to adjust the talent; however, this just caused AC to be the only option.
It’s not possible to correctly balance two pets versus the one pet option. Two pets increases the amount of procs and speed of damage.
Blizzard’s concept of BM is utilizing two pets for optimal damage.