I hope you don't mind me moving things around a bit.
Dude, that was like the first thing I said in this thread!
If you want to have a setting where music is the source of magical power, then do that, but it doesn't need to also have wizards and clerics in it. If you add in too many discordant concepts together, then you end up with The Forgotten Realms.
I have gone back and read your first post, which I will not bother quoting for the sake of space, but I still don't find it particularly convincing. In fifth edition, words of power (and music, by extension) is
a source of magical power, but it is not
the source of magical power. The approach that 5e takes is that there are multiple paths, philosophies, and flavors to magic (or the Weave). Sure the bard may have been "part wizard" in 2E, but that was also in the days before other arcanists, such as the sorcerer and warlock. Since then, the wizard's monopoly on arcane magic has been (thankfully) destroyed.
Furthermore, your original statement that marginalized the musical magic of the bard does not even make much sense in the context of 2E either. In the 2E PHB, for example, this was our first description the bard:
The bard is also a rogue, but he is very different from the thief. His strength is his pleasant and charming personality. With it and his wits he makes his way through the world. A bard is a talented musician and a walking storehouse of gossip, tall tales, and lore. He learns a little bit about everything that crosses his path; he is a jack-of-all-trades but master of none. While many bards are scoundrels, their stories and songs are welcome almost everywhere.
We get lots of music talk in this. Furthermore, the whole wizarding and spellbook approach of the bard felt a bit slapped-on, IMO, since the text refers to them as dabblers who pick up their spells more through "serendipity and happenstance" rather than study as per a wizard. The speaker even says that the bard uses their spells to "entertain and impress" as an extension of their performance.
The bard's approach to magic is similar to an artist, a dabbler, or a dilettante. It's "some" here and "some" there. The bard studies some, picks-up some knowledge on their travels, and some of the flavor text kinda implies that they mimic the power of the gods or at least the echoes of creation, which may explain their access to divine magic.
The bard has the liberal arts approach to magic. If anything, the bard is even more of a magical dabbler* than they were in 2E.
* More in terms of breadth. In some respects, the fact that they now can cast 9th level spells, recasts the emphasis of their magical dabbling.
Musical magic doesn't jive with the established concept of magic as an inherently academic concept. Adding in another source of magic is just unnecessary complexity for a setting where we already have wizards and clerics.
Except that it isn't established at all, unless one privileges wizards as having the sole "true" concept of magic, which is exceptionally outdated in D&D. (But this may yet again speak to the privilege and double-standards granted in favor of the magic-user/wizard.) I don't think that one can reasonably argue that magic is inherently an academic concept when magical bards, warlocks, clerics, druids, sorcerers, rogues, fighters, rangers, paladins, barbarians, and monks all exist in this game who all have different philosophies and approaches to magic. Only wizards use tomes for their spells and magical studies, apart from ritualists and tomelocks, who get theirs from their patron. Bards have certainly not "devolved into is just a jumbled mess of pointless high-magic mumbo-jumbo that doesn't make any sense outside of the Forgotten Realms," but, rather, they have evolved and expanded just as magic in this game has. And I would also argue that the 5E bard does make plenty of sense in many settings outside of Forgotten Realms (e.g. Eberron, Planescape, etc.) though not all (e.g. Dark Sun).
It seems bizarre to say that the bard's approach to magic is inappropriate for a "serious game." That seems to involve an exceptionally narrow sense for what constitutes a "serious" game (of grown men pretending to be wizards and warriors fighting dragons), and, again, I suspect it's one that privileges wizards as having dominion to the truest expression of magic. A bard's magic says nothing about how "serious" the game is. It only says anything about how one envisions magic in a particular setting. If your homebrew setting does see magic as pure knowledge, science, and nerd-power-play, then I can see how the bard's magic can certainly seem inappropriate to the homebrew's aesthetic, but as per D&D's default assumptions for at least three editions? Nope.
