Agreed. Every 1st party character can supply a full pack. Smash Bros. rarely scratches the surface when it comes to music. Yes the game has over 800 tracks but a lot of the music comes from a very small selection of games in a franchise and a lot of the songs are remixes of a single tune (looking at you Jungle Hijinx and Zelda Theme). Also with how vast and long lasting a lot of Nintendo's franchises are you can never run out of stage ideas.
I can even provide a few exanples:
Dixie Kong - Comes with a minecart level, a bramble level, a honeycomb level, a frozen DK island level, any stage based off of DK: Tropical Freeze basically any level thats not a generic jungle. As for music. DK has some of the best music in all of gaming yet Smash barely scratches the surface. You can pull music from DKC3 which has no tracks, Tropical Freeze which only has 2 tracks, Barrel Blast which has no music (got removed), DK64 which has no music besides the butchered DK Rap, and Jungle Beat which only has 1 music track.
Bandana Dee - You can literally choose a stage based on any modern Kirby game because their is none. Also while Kirby IMO has a fair amount of music tracks that are varied their is still a ton missing in Smash mainly from once again modern Kirby games. Also its not like Bandana Dee is short on material to work with considering their is a new Kirby game every year..
Captain Toad - Represent a new franchise and while a lot of Captain Toad's levels are based on 3D Worlds levels/assests. It shouldn't be a problem in Smash because 3D World doesn't even have a stage based on it in Smash. Its the only 3D Mario game with no stage representation in Smash. Captain Toad could come along with both a stage based on 3D World as well as Treasure Tracker (it would also tie in nicely with the upcoming Switch port). As for music their is only 2 3D World tracks in Smash (Super Bell Hill and Bowser Battle) I believe. Captain Toad could not only come with the few original tracks found in his own game but a bunch of 3D World music as well.
I have other exampales=
Vaati - Comes with Vaatis Palace or Dark castle Hyrule and can use Tracks like:
Vaati Boss Themes Phase 1-3
Temple of droplets
anything from FourSword and Adventures
these 3 games Minish cap , Four swords and Adventures have only 1 Track that is a Kakriko Remix
Spirits: Vaati (Mage/Fighter Spirit) Vaati (Boss Form 1 and 2) Statue Vaati and Shadow Link(four Swords Adventures)
Dark Matter (kirby)=
Stage= Another Dimension, Darkcastle, Darkstar, Ripple Star or DDD Castle (DL3)
Music:
Coo, Rick and Kines Theme Remix
Darkness Returns
Masked Dedede Remix
Mecha Knightmare
Galacta Knight Remix
Spirit : Dark Matter (True/FS), Zero 1 and 2 and Adeline
Here is a Bandana Dee Fighters Pass Idea
Fighter: Bandana Dee (Duh!)
Stage Dedede Arena (Superstar
ULTRA) or Dedede Castle or Halcandra or you get the Idea
Music:
Coo, Rick and Kines Theme Remix
Darkness Returns
Masked Dedede Remix
Mecha Knightmare
Galacta Knight Remix
Apple Juice (instrumental) Remix
Kirby Star allies Void Termina All Phases
Boss Theme Medly 2
Spirits: Bandana Dee (Parasol new Fighters Spirit) Dark Matter (True Form), Zero 1 and 2, Taranza, Star Dream, VoidTermina( Humanoid and Soul), Hyness, Shadow Kirby(KF2) and Adeline
If you Want to Know more about Kirby Meteorz is on Youtube! (little Shoutout)