That reminds me of one of my favorite scenes in Amadeus when Mozart shows up Salieri by playing a Salieri composition. link
Basically, Lang Lang takes it to another level - which is understandable given who Lang Lang is.
The use of such a horrible word says more about you than it does about them. I don't know if Frederick composed guitar solos on piano, but the best-known piece for classical guitar was composed, possibly on piano (I'm not sure), by someone who wasn't a guitarist. So, yes, you can compose oboe lines on piano, you can compose trumpet solos on guitar, you can compose singing parts on saxophone.
At the end of the day, many (most?) composers write music in their mind, and then use an instrument (not necessarily the same which will be used for the execution of those bits) to explore that music further.
sounds like a perfectly reasonable response to an extraordinarily unreasonable post!
it's quite possible that bucsateflon may not actually know how an instrument functions. that's just derived from this comment - guitars, pianos, violins, etc all share the same basic principles.
What's interesting, is how Roger was able to compose the riffs, melodies and guitar solos to his songs using nothing more than his drum set. Now there's something to think about. "No, no, no, Brian... it should sound like this: duh-duh-duh-k-shhhh.... duh-duh-duh-k-shhhh....pow-pow-gun-dun-dah".... "oh you mean like this?" ... brian plays solo to a kind of magic right on the spot. Now ....that's how you do it, folks.
At the end of the day, it's not so much 'writing guitar parts' or 'writing vocal parts' as it is 'writing music, which is later executed on guitar or oboe or trumpet, etc'.