We agree. Post 10, point 1. I call this lame verisimilitude: You wave your clarinet, as an arbitrary restriction, and playing it is irrelevant.
If you're a full-caster, and you have embraced your role as a full-caster, then why are you trying to pull off some wacky martial shenanigans? The Bard is a versatile class, but it can't be all things at all times.
I don't see a problem. A wizard or sorcerer that uses a shield or carries two weapons is in the same boat.
Do you mean that its sloppy because a bard instrument requires two hands to play whereas an arcane focus only needs one hand?
If you wear a shield then don't play an instrument in combat.
Or use a horn. Or use a spell component pouch.
I say just ask your DM, and whatever he/she decides just go with it. If they want to hand waive it, that's fine too. Nothing will break either way.
Maybe you are mistaken on the concept? It's not like there's any magic inherent in the music or anything. Bards cast spells because they learn a little bit of everything, and magic is a thing that they can learn. They have a party trick that lets them cast spells while playing music, in case they don't want to reach for spell components in the middle of a song, because music is another completely separate aspect of their portfolio that they don't want to neglect.Sure, you might prefer this method of casting spells in the middle of combat, but the fact remains that the concept of the class is that the character is a musician and it's kind of silly that rules prevent you from using your instruments to cast a spell but allows you to use a component pouch.
...and that's the other thing ...the main one in fact. The Bard (while wearing a shield) CAN cast all spells with Material components if he's not using a spell focus, but using a component pouch instead ...So basically, the rules makes the Bard (a musician) more effective if he doesn't play musical instruments and is played as a "wizard" instead ...
If they wanted to create a class that channels magic through musical instruments (which they obviously did), they should have facilitated this by making it possible for the Bard to cast spells the way it was designed to, which is playing an instrument, and not penalizing the character for doing so !
If you want your bard to use an instrument in combat why are you using a shield I have to ask. Many other classes can use shields but lots of characters don't actually do so. Its only an option. For your character I would drop the shield and you will be able to play in combat easily.
[MENTION=6775031]Saelorn[/MENTION] I don't think bards have a "party trick" that "allows" then to use music to cast spells.
The jack of all trades schtick goes way back to Ad&d bards who HAD to multi class as Fighter, Thief and Druid - hence the theme.
However...
The PHB says
The bard is a master of song, speech, and the magic they contain. Bards say that the multiverse was spoken into existence, that the words of the gods have it shape, and the echoes of these primordial words of creation still resound throughout the cosmos. The music of bards is an attempt to snatch and harness these echoes, subtly woven into their spells and powers.
It then goes on to mention "the magic hidden in music".
It's not a party trick, it's their raison d'être.
I think this is the sticky wicket of the discussion.It's not like there's any magic inherent in the music or anything.
...
At least, that's how I see it. Maybe there's a huge call for magical musicians, and everyone else expects the Bard to be that. It's hard to say what other people may be thinking.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.