Bitter taste of rocket pesto
Rocket has an inherent bitterness and not much sweetness, so any pesto you make from it will have that quality. You can try and balance it with sweetness, acidity, etc but that will only go so far. Basically, if it's going to be too bitter for someone's taste you're better off making something else, or using the rocket's strong flavors in conjunction with something like coriander leaf, cilantro leaf or basil.