On the editorial side, LilyPond is an incredible tool for creating modern editions of earlier music, specifically music in mensural notation. It comes with common glyphs and has full ligature support, and the separation of content and presentation means that one can reproduce the look of early manuscripts and prints while generating a modern score from the same source file. This has been really great at reducing transcription errors by easing the mental burden of transcription, transposition and note reduction, which can all be handled automatically by LilyPond. It's not perfect, but miles ahead of any alternative.
What older people on the extreme of some skill think about the skill is not necessarily applicable to 99.9% of us.
It requires a tablet and pencil/stylus, and it’s a bit pricey. But I’ve found the handwritten interface, once I got used to it, to be fairly intuitive.
My still-early impression of StaffPad is that it is best for writing scores in a traditional, classical-like format, and detailed knowledge of standard music notation seems to be necessary. It might not be suitable for people who are more comfortable composing with keyboards, rhythm machines, digital audio workstations, etc.
I learned how to write music 50 years ago on paper. Compared to that, this software is a huge advance. Being able to edit scores easily and hear what I write played back is wonderful.
There's definitely room for something that bridges the advantages of the different approaches, but it's a difficult problem and it's a $0 billion market, so having passionate people make MuseScore better is probably the best path forward.