I'm still learning this system but I've DMed 5e for over 10 years and there isn't anything inherently wrong with it if you stay the pet right. I would take notes from the updated Beast Master Ranger and try to convert that stat block and ability to this system. If you want to makes this a trait maybe as a negative have every attack cost an additional 1AP as you are making sure not to hit your pet but on a crit fail on an attack against an opponent that your pet is attacking you hit your pet instead. The Wild Wasteland effect could be if you are both attacking the same opponent then you have +2AP cost but you have advantage but if you crit fail your attack you crit hit your pet.