Our fuel had sulphur not an octane problem, so I doubt it was detuned.
I have had a chance to try an European ECU together with Lambda sensors on two of my cars, the 540 and the M5 an on both I ended up putting the South African software back because it felt better in terms of power. The Euro software made the engine smoother and more refined but less driveable.
Depending on the year some cars had no cats allowing the SA stuff to be tuned for more power, though this was not published.