No doubt. If you spend some time with them you can rehearse them to the point where you can play them reasonably smoothly and with ease. However, you seem to have missed my point. It is not that what you wrote is in any way illegal or is so difficult as to be unplayable, but that it is disproportionally difficult compared to the musical effect. It is a modest idea and the difficulty spike seems absurd with regard to what is happening in the music. Tell me, is adjusting the music in a non-essential way so that it lies better and gives the instrumentalist a greater chance of expressing the underlying form really such a large compromise? It is so wasteful to refuse to optimize even if you have virtuosos at your disposal (which most people do not). A similar thing occurs in programming - people know that they have an exorbitant amount of resources at their disposal and adopt dubious practices because they can get away with it. I think it is bad artistry - and you bet that people respect for example video games with solid engines that you can max out on modest hardware without a hitch. That's a sign of quality - and it comes at no expense to the precious artistic vision of the developers.
Beethoven is crazy, almost as crazy as the music he writes. He paints broad strokes and seems to ignore the canvas completely (was there even a canvas to begin with?) - in this sense he is similar to Béla Bartók. His string quartets are hideously difficult. I do not know any music which is as vehemently uncompromising, at times dissolving into almost complete barbarism. This is the spirit of the music, and it is hard to argue that he should exercise more civility when writing for strings - it seems almost a paradox to suggest so. Your music is not that crazy, in fact it is quite modest and well-mannered. In any case, both composers were reasonably aware of what they were doing, and you do not find many examples of such needless difficulty. When something is difficult, it is because there is really a lot of urgency or because it is to achieve an effect which cannot be achieved otherwise.
I do not understand your reasoning that because you do not hope for the piece to be performed that you can allow yourself more liberties. Strictly speaking, it isn't music until it is heard in performance - just imagine if you didn't have Sibelius playback. The concept of "writing for an instrument" without writing for it is puzzling to me.
That is a valid position to take if you believe in it. Personally I choose to look at it as a collaboration. I like to write music and I like to play music. I like to play difficult music, but I don't like to play music which is difficult solely because it is ignorantly written. Part of being a professional is being able to be on your A-game even when you are handed awkward music, but as I am not a professional performer I do not have to deal with that and greatly appreciate when things are cleverly written. My experience singing in choirs and playing in orchestras has led me to realize how important the psychological aspect of written music is. There are certain pieces where I can reach up to a chest G4 (sounding) with relative ease, like Rachmaninov's Bogoroditse Devo (but I have only once been brave enough to go all the way) from the Vespers and then there are others where I struggle with B3 (the difference is purely psychological, when testing my range on the piano I have reached up to B5 in full blast). It is symptomatic of me not believing in the music and not feeling it believes in me, if that makes sense. The Rachmaninov piece, although it is only an example, is special because it is written so comfortably for the voices. More important than being comfortable, all of the parts are interesting to sing and I really feel as if the composer is welcoming me to sing the music. This is something I consider very important, and it makes the performance instantly better. I especially love to sing music by the old Renaissance masters - it gets to be quite tricky but you always consider it an exciting obstacle to overcome - at least I do, they were real pros.
Don't misunderstand me, I have nothing against difficult music nor do I advocate unreasonable compromises. I would say that my music is generally speaking difficult and I have a few embarrassing experiences to confirm that. I have also written my fair share of absurdities due to misinformation and am in no way perfect. Anyway, I think the composer is responsible for their performer's emotional and physical state while learning and performing their piece. It is not a responsibility to take lightly - they aren't machines.