Pinkie Pie: Alright, we're gonna go all-out! I'm talkin' marching bands through the streets! Front-flips! Towers of ponies! Choruses from every window and rooftop!
DM: Honestly, it makes a certain kind of sense. This particular Ponyville dimension is predisposed to break out into sunny showtunes. And what kind of song are they singing?
Pinkie Pie: I dunno. I never really figured out music theory.
DM: ...What?
Pinkie Pie: I mean, Pinkie Pie probably knows how to compose a ditty on the spot, but me personally? Why else would I mostly do song parodies and poetry?
Ah, poor Pinkie. Gotta admit though that so far Pinkie's player did a nice job of showcasing a bard regardless. That's usually the key, you can always try to remove your limitations, but it's usually more efficient to just avoid the pitfalls altogether by keeping to what you do right. Alternatively, there's also the creatively empowering option of working around one's limitations by tweaking one's strong suits into masking said limitations.
And Tim Minchin, and Victor Borge, Tom Lehrer, the Marx Brothers...
Just count the number of comedians out there, then count the number of musicians, then count the number of comedy-musicians. You have a quantifiable example of how difficult it is!
Spike Jones was an absolute sensation back in his day. There really wasn't anything like him before besides perhaps a few vaudeville acts. His 'orchestra' would often play the first bit of a song completely straight, to prove that yes, they are talented musicians who know how to play. Then the wacky kicks in and goes up to eleven.
And Jason Steele. And to preempt any arguments, yes he is primarily a cartoonist. But a wide majority of his cartoons contain original songs, and they are always amazing.
In the show, there's a full-time composer who studied and practiced for years writing songs for Pinkie to "spontaneously" sing. No real person is that creative. Even prodigies like Mozart had to take a little time to write things down and tweak them.
Given Pinkies penchant for preparation, I have little doubt that she has no less than 200 compositions for everything from short tunes to full-on rock operas in her personal Batcave