Bike shops randomly stuck reflectors into the wheel spokes of hundreds of thousands of bicycles for decades, and nobody ever said that the reflectors caused any imbalance problems by being there.
More than a few somebodies did including me. The three bicycle shops I worked in required you to put the wheel reflectors opposite the valve stem and quite a few customers whom I would guess had bought there bicycles from one of those other shops who randomly placed the wheel reflectors anywhere they felt like also complained about discomfort at high speed until the wheel reflectors were moved or discarded. These were usually people with the lightweight bicycles who rode many miles. Some including myself refuse to use wheel reflectors. The problem is only noticeable at high speed.