I don't believe any synthesiser is limiting. It is interesting how there can be several points of view on something. They are limitless rather than limiting. Presets are a great starting point to get to know the sonic capabilities of the instrument. And also to inspire. They certainly do that for me. Reverse engineering of a preset synth patch enables you to learn the basic principles of synthesis. Once you have some basic understanding of the concept of sound building then you can easily learn what the original programmer did to create that sound.
You can now edit any aspect of that sound and turn it into yours. Waveforms can be changed, within minutes if you want you have a totally new sound that is yours and very original. All from a factory patch to start.
(the Roland Jv30 is the best General Midi synth for sound editing direct on the front panel) Editing factory patches is great because you start with something half way there and end up with something that is fully there and very original. Roland synths have always made it easy to edit sound parameters.
(The JD 800 is over the top with a faders and rotary controls and switches for every parameter laid out in front of you) The sound editing part of the Jupiter 80 looks pretty deep too.
Or you can build from scratch and create the sound yourself using the vast storage of raw materials you have to work with. Imagine pressing a key and hearing 16 events take place. All in their own time and space, some at the same time to fatten and add interest to the sound and other parts delayed and layered in. It doesn't take long to build a complex ambient texture for example. Different parts of it can be mapped out over the keyboard and velocity switching can bring in new sounds etc. The performance options once you have a sound made are also enormous. Adding in after touch, pedal, breath control, ribbon, pitch and mod wheels, the 10 sliders on the front panel of a Kurzweil etc..It is all about sound programming and how that is done in relation to the velocity curve of the keybed.
The keyboard is also a great performance instrument and for those who can play it well it is a super expressive tool. I think the synth action is also well designed because it is no less expressive than anything else. It allows for a different playing approach. With all the extra bits you can add to a performance keyboard in terms of performance controllers it is still a very expressive instrument. And for those with a deeper understanding of music, it is well organised.
PS the real power of the Kurzweil is using the editor software. Then the GUI takes on a whole new meaning. Those screens are large, detailed and look great and you can deal with huge amounts of stuff on one page. That is how you use it in the studio. The editor even runs fine along with your DAW and it has a two way link to the instrument. This editing program that is normally $99 is free currently to Kurzweil buyers. On stage you don't need it. It just sets up all your sounds and organises things into a very fast and retrievable system that uses the built in display. I find there is more than enough info on the display.