Your argument doesn't hold water.
The classical pipe organ, often referred to as "the king of instruments", is a synthesiser. The organ console is an electrical or pneumatic controller, with no direct connection to the pipes. Most large organs have considerable "latency", due to the distance from the console to the pipe room. Some pipes may be as much as a hundred feet away from the player, so the sound will take over 90ms to reach them - several orders of magnitude more delay than a modern computer system.
The organ is still regarded as a highly expressive instrument, in spite of the relatively modest control a player has beyond simple pitch and duration. Although most organs have many stops which provide similar timbres to existing instruments, it is understood that the organ is an instrument in its own right and should be played as such, and is not merely a tool for emulating other instruments.
The idea that an electronic instrument should imitate acoustic instruments is simply a poverty of imagination. Electronic instruments, used in a manner that is sympathetic to their natural properties, can be absolutely as expressive as any acoustic instrument. The theremin has perhaps the worst user-interface of any musical instrument as the player has no physical contact with the instrument whatsoever, but is utterly beautiful when played by a master.
The challenge for electronic musicians is that they are often both performer and instrument-maker. A monosynth of any quality can be configured in a near-infinite variety of ways, many of which were completely unforeseen by the designer. Musicians working with modular systems or DSP programming environments have a blank canvas. We do not as yet have a good theoretical framework for this task, but electronic music is extremely young - no more than ninety years old at most. We are only just beginning to scratch the surface of what is possible.