Not to challenge you, but this makes me picture that a bard would have to wield both their weapon AND instrument if they wish to function in combat the way a bard does. And to the nine hells if the bard uses a bow. It's just a rather silly image: Bard of Swords, scimitar in hand,
— Benton the Bard (@Hero_of_Limes) May 22, 2018
and fiddle, or lute, or harp, or flute, etc. in the other. This picture does not strike me with grace, finesse, or style. Not to mention that a bard who plays with two hands can’t play at all in combat, unless they don’t combat in combat. Just saying. Respectfully. The rules don't require a bard to play a musical instrument to cast spells.
— Jeremy Crawford (@JeremyECrawford) May 22, 2018