Yes, it’s all MIDI. People complaining about it are ignoring the fact that it’s beyond ubiquitous and has not required a change for literally decades. It’s a smashing success, warts aside.

The dude replying to you with “Sibelius” apparently doesn’t understand that, like all other DAWs and notation programs…Sibelius uses MIDI, because of course it does.

Not the parent, but some limitations are that you can only really have events that describe channel/time/value. That's mostly fine for instruments like piano. But on a guitar you can pluck the string with a soft/hard object, close/far from the bridge, add vibrato to an ongoing note, etc. Sometimes it's enough to use multiple instruments with different characteristics to simulate that. Sometimes not.

MIDI is fine for some instruments and for controlling few high level parameters. If you want to make music though, you'd go with a DAW instead which can start with MIDI on some tracks, but otherwise works with waveforms instead.

There's also a difference between when you only compose, want to hear the idea put together and give musicians the sheets, and when you want to create the end result fully on your computer.

EDM artists work within the limitations that their tools provide. There's a reason that you hear synthesised/sampled pianos all the time in electronic music, but rarely synthesided/sampled guitars: midi sucks at expressing guitars.

There are some really great guitar sample packs out there, I particularly love the Impact Soundworks Shreddage series, but just look at how much they had to mangle MIDI to make it feasible, with NINE (9) sections of the keyboard dedicated to mode switches, and chopping up the velocity space into five different articulation modes, and they still can't model unison bends which are a staple of classic rock guitar: https://www.youtube.com/watch?v=P2h9AmL2BhI

edit: actually after double-checking, they do support unison bends, but it's a special CC parameter that you have to turn up to do the technique and then turn back down when you don't want it anymore, pretty hacky. The point is, you can't use MIDI to actually play these instruments like real guitars live, even though these sample packs can produce realistic guitar sounds, you need to do butt-tons of midi programming in ways that MIDI wasn't intended to be used in order to make it sound mostly right to the point where it's probably easier to just learn to play the instrument than put in the extreme effort of meticulously programming all this faff.

Sibelius

I'm not a composer but I imagine .sib and PDFs

I thought midi was more intended for live messaging between different instruments/controllers