I think Bard is a celtic word via the Welsh, so I just picture Sian Phillips dressed up as some kind of ancient Gaul-ish witch hehe.
It'd be a cool idea if Bardic 'magic' had a certain aspect that was inverted from the norm, so when the crowds are larger then the spells are somehow more likely to succeed or more potent. Or basically that the power scales depending on how many other Characters or NPCs are around. The more targets the better.
Whenever I picture any sort of actual Bard from history, I just assume they had super elaborate stage production and were essentially the rockstars of their eras. Like some sort of Grateful Dead show, where having more heads around has particular mechanical advantages that emerge. So similar to that situation where the fighter is taking on that horde of goblins or lvl 1 monks, but where if you have a Bard on board when that happens, the trash mobs become crash mobs, and can then work to the party's advantage. To turn the tables and invert the usual dynamic, where more random enemies or bystanders means more problems, here it would be like a boon.
Again, not unlike how Clerics have turn/control/destroy undead as a situational ability, doing the same thing for the Bards in a big AoE type burst. Basically the whole thing should be more AoE I guess, so less specialized target but more the randomized table thing (maybe like what we got from Wild Magic, or the Sorcery sub-class in the current edition). Some spells work this way already I guess, the hypnotic patterns and various crowd control stuff coming over from the Arcane lists, but they could definitely be made more bard specific.
I also think there is plenty of room to drift into the Druidic origins here, and craft a spell list that is unique but which hits the hallmarks. Mighty Morphin' Polymorphing changing into an animal, even a fish, or anything that's like Pied Piper centric. I think there are some things that could lean into choosing voice or a sound, not that bards need to be musician exclusives. To me the key aspect is the story-telling, but since instruments ended up being pretty cool in BG3, I could imagine instances where the bard maybe chooses a Reed instrument and that's like associations with the wetlands or rivers, swamps and marshes and birds. So that Bard might have a whole Crane Bag circle, that leans more magical. Wheras another type of bard might take up the horns, or the strings, or the drums, each with certain animal or plant associations depending on the materials used to create those instruments. Like they all come from animals and plants basically, so that could be part of the Charismatic extension. Like where you need the group or the environment to help make that magic work. Even if it's Magic Paintbrush style, where the animals and plants come to life and take part in the song, cause that's pretty classic. Like it's the whole Apollo/Orpheus motif going on.
Just like Druids and Bards used to need high CHA to be available as a class choice with that as secondary stat requirement, I think it makes sense that there is overlap, but having a completely unique list of spells, with different forms of canting (even if the ultimate effects end up similar) would help to make everything more harmonious. In the latest iteration, things do feel sorta all over the place, like Class fantasy got the real Mr. Potato head treatment, mix and mash.
I think the hybrids are fun, but the more of them there are the harder it is to just play as like a regular rescue Ranger or whatever hehe.