If Hans Zimmer, composer of the most robotic orkestral compositions (that require no expression, nuance, or variety for their execution, and which are further complemented/distorted by being blended with synthesized sounds), who has not just the best, but ALL samples available on the planet (including his own) and can afford the best programmers and studio apparati in the world, if a man of his aesthetics and tastes still engages a real orchestra to perform his locomotive drones, that says something, loudly.
Nevertheless, you refer to "pure expression of musical ideas", bereft of any performer's input. I cannot refute this of course, since only a mechanical device programmed by the composer can come the closest to this particular ideal today. Add to this the efforts on behalf of the programmer to simulate 'Realism' in that performance by using the best samples available to him, Impulse Responses and filters and whatnot in that strife for purity (so no 'Humanizing' features I presume, or any feature that would reflect a real performer's chance, inadvertent deviations...)
Like I said, one cannot argue against this, simply because it is a matter of preference. The same could have been said 30 years ago with the technology that was available then. It doesn't matter that sampled performances sounded inferior compared to good live performances (they still do today, only less so), a composer -such as I was back then- could still contend they preferred the simulation, for it expressed my musical ideas purely. This principle could be further extended to the Casiotone, or a Pianola further back. I don't know whether Debussy would take that over Michelangeli.
Now if you argue that today we have more control over more parameters of performance than we did then -therefore our results are closer to that "pure expression of musical ideas"- then I'll say you're right there, but that expression is not pure yet, it will keep getting purer as technology and individual programming skills keep improving.
To me, samples still sound like what they are, just better than before. At best, as with Bacal and others, they sound glorious for what they are, and I marvel at the programmers' abilities to get this much realism, and generate quasi-living musical organisms out of neutral, mechanical sound molecules.
Additionally, I will say that if for some reason I was only allowed to keep only one version of my each orchestral composition thus far (simulated vs. live), in most cases I would keep the simulated one, only because they are better in many respects to the live performances. However, that is because the live performances were so far below par. Were they par or above, I would opt for those instead, as a) There is no fakeness in the sound which hugely detracts from the overall enjoyment of the work, and b) The music sounds alive, breathing (it sounds so in the bad performances as well, but sick and dying unfortunately). Sadly, the main issue is that the fakeness in sampled performances is most pronounced in the strings, which are the most important section and half of the orchestra. I am sure this shortcoming will be ameliorated in the coming years/decades. As we stand now, I have to say I am unable to make that 'leap of hearing' and pretend it is actually an orchestra performing and not Cubase. It's not even close. It's like in that other thread with the trio(?) where we are asked to pick which version we prefer. I immediately went for the live performance, I am suprised that it was even a question since the simulation was not good; it sounded very fake and plastic from 'Go'. I am only mentioning this since I too am not a great programmer.
Finally, I have experienced quite a few instances where performers actually improved on the purity of my musical ideas (ex. change of tempo in a section, rendition of a line, etc.), and I would be sorry to have missed out on those. And if you remember, I ended my post with the idea that we have not been put in a position where we have to choose between one world or the other, but in one where ideally we can take the best of both.