The R6S is NOT detuned, but it IS slightly older tech and was created when supersports were not pure track tools. It was the best of the best in 2003 (and again in 2005 with the new fork, tire, throttle bodies, brakes, and rear link). The modern R6S has the chassis of the 03/04, and the engine of the 05. If you have never ridden a supersport or faster bike, it will be terrifyingly fast at first.
It is more comfortable, torquier, and (unlike detuned bikes) equal in weight to the R6. It has lower peak power, less aggressive rider positioning, and slightly less sharp handling (though still extremely quick, and AS quick if you set up the suspension). At a trackday (rather than a race) it is essentially equal to any modern 600.