As for the "half-caster" question, above... For me, it is a combination of two things. One is flavor/concept for the class. One is simple meta-game design space.
One: Bard's started out as part druid, and should never have been made wizard/arcane casters. They got spells as druids, but that was after many (somewhere in the neighborhood of minimum 10-12, from what I remember) levels of something else. Making magic/being able to work magic or have magical knowledge is definitely a PART of the Bard. But it is not -and should never have been set up as- the primary part.
The second is, just, since WotC went that direction (of having the Bard be all Arcane-focused), it was an obvious missed opportunity, and asymmetrical in a game with FAR too many "full casters," where you have the: Cleric and half-(divine)caster warrior Paladin; the Druid and half-(nature)caster warrior Ranger (which, don't get me started on 5e's spell-slinging rangers); there was a BLATANT opening for there to be the Wizard(or Sorcerer) and the half-(arcane)caster warrior Bard. THEN, Bard could have been morphed into some combo/subclass of the greatest missed class opening for all of D&D's history - the fighter/mage combo-class... And they somehow missed (or ignored) it.
And for a third, as others have said, the Bard is really what is supposed to be the ultimate 'support" class. Need help fighting? Look to the Bard. Need help skulking/picking locks or pockets? Look to the Bard. Need help talking your way out of some trouble or negotiating a contract? Look to the Bard. Need some (emergency/little bit) healing? Look to the Bard. Need a spell? Decipher some hieroglyphs? Identify some magic item? A little bit of luck? A "Hail, Mary!"? Bard. Bard. Bard. In a pinch, the Bard can help do just about ANYthing that a party would need in a life of adventure. Can't do anything the BEST! Can't "out-fight" the fighter or "out-stealth" the thief or "out-heal" the cleric...A wizard is "the best" at magic/casting spells. The Bard , really, can not/should not be "as good as" a wizard at arcane magic.
So, far as I'm concerned, half-caster is the BEST at spellcasting a Bard should hope to have. The class has plenty of other magical powers, mundane tricks, myriad skills, oh yeah, and there's still weapons to use when a bard's player is looking for something to do on their turn. "Full casting" has no reason to be in a Bard's very-well-packed quiver.