You come up with some awkward questions, PeterthePapercomPoser! : )
It’s both, a damned tribulation when the latter, relaxing when the former. Unfortunately the balance seems to fall toward the latter these days. My latest bit was a challenge (to grow). It failed and through 10 versions has become an ordinary modern programme piece.
Of the many issues you list, most of the weaknesses fall my way most of the time. For example, Struggling with writing good melodies. Even motifs give me a headache, evaluating if they’ll work / can be developed. Aside from light music I avoid formal melodies because they come with the expectation of meter of some kind, not always easy when one regards a “phrase” as a whole – the tune, harmony, scoring, overall change of dynamics, interplay of lines and on. Fine if you’re writing tonally with cadences available that meet expectations.
The first item that turns out a strength is not using too much repetition. I’m no fan of it. In fact when I look at a score and see those double dots at a double barline I think ‘Oh no. I’ve got to listen to that bit again!’
Orchestration – while I still see the orchestra as a machine I tend to treat each instrument in its own right, having its unique contribution which makes some of the bureaucracy of orchestration difficult. I hear music inwardly as orchestral so I have trouble writing for solo instruments, particularly piano.
I’d guess we all suffer some of the list as weaknesses at times and at other times strengths. It isn’t always easy to translate what’s in ones mind to an art medium. I have a reasonably good ear to transcribe a melodic/motivic fragment to paper but the subtle orchestral sounds - they take effort (and I hope not to lose them in the process). Then the problem if you like through-composing is often “what happens next”.