My thoughts exactly, but even just a few 'real' instruments can tax even a fairly powerful computer when you need audio streaming lots and lots of small files, all the time. Not to mention the 'beating on the HD' issue when it's encased in a keyboard...
And, of course, there's the final nail, for me... I LIKE tweaking my styles. I like the ability to try a guitar part with a nylon instead of a steel string. I like to tweak the attack and decay, depending on tempo. I like to try the style with brushes instead of rock drums. I like to try tablas instead of congas. I like to be able to make the style MINE...
If a style is NEARLY perfect for a song, but a kick in the guitar part is wrong, or a drum accent is mistimed, I can edit a MIDI style.
You can't do this with an audio file. Everybody that plays the audio based style parts are going to sound IDENTICAL to everyone else's, whether you care to tweak or not...
No, the way to get 'realism' out of a style is not to use audio loops. It's the easy way, the quick way, the preset way. But realism can be achieved with MIDI also. It just involves massively more ROM for the sounds (to get close to GIGA quality), and more elaborate NTT's and rule-based behavior for the patterns. Imagine a cross between Yamaha's SA voices (for note transitions and intervalic rules), Korg's and Roland's Guitar Mode (for more accurate NTT's and instrument specific behaviors), and MUCH larger ROM for multi-velocity sounds.
These are capable of achieving close to audio loop quality, but with all the advantages that MIDI allows us (larger chord choices, editability, smooth transitions).
The GIGA-based arrangers (Wersi and MS) are showing the way (but MS seems lost in loop-land, for now), but seem unable to finish the job, relying on the user to select (and purchase) the GIGA sounds, and do all the work tweaking the styles, working out your own NTTs, etc..
If Ketron want to find a use for (hopefully) robust disk streaming, perhaps just GIGA sized MIDI instruments and more work on advanced NTT's might be a better choice.
It would certainly be a more FLEXIBLE choice...
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An arranger is just a tool. What matters is what you build with it..!