IMO, the issue is with the term "bouncing", to me that means both feet lifting off the ground and head moving up n down. Anytime both feet leave or separate from the ground you lose your base. No base = loss of mobility (reflexive/reactive movement) and the ability to generate any meaningful power. Defined this way, "bouncing" would limit you both offensively and defensively, so yes, it is a flaw. However, being "light on your feet" I don't see as a flaw at all, quite the opposite. Hence, technically refined fighters who are considered mobile, don't "bounce" (I.E: Lomachenko, Rigo, Sugar Ray L).
The difference between the two, being light on your feet your weight isn't moving up n down (bouncing) it's subtly shifting hip to hip and you are keeping constant contact with your base and not compromising your mobility or sacrificing the ability to quickly set and throw a meaningful shot. Being "light on your feet" or mobile, in a technically correct way wouldn't have your head moving up n down, instead it'd move back n forth or in a "swaying motion". I.E: standing on a tire and shifting weight hip to hip correctly, your head should stay on a even plane vs up n down.