The Golf's brakes could be better, but then the type approval parameters by which they're selected I'd imagine only require a finite number of stops and not repeated hard use. In the use my car sees, the only time I've found the brakes particularly wanting is with a car trailer on the back, but then my pads are original at 5 years and 46k, and have half pad thickness remaining (must be driving too slow). I'd say the brakes are certainly no worse than comparable vehicles (330ci, Clio 182, Impreza, 130i, S15) I've driven recently. I wonder how many cars on this forum with original calipers and 312mm discs have decent quality consumables fitted.
Had there been an option from factory to have multi-piston caliper with floating discs, I wonder how many buyers would have ticked the box. I suspect many wouldn't and the marketing team know this. Very often (but clearly not in all cases) I suspect a GTI is not originally bought by an "enthusiast", but someone who likes the image of a Golf with a GTI badge. That said I wish there had been a factory option for uprated brakes and an ATB diff and that the first owner of my car selected them!
As for the engine debate, I'm suspecting engine type approval and OEM development costs meant it was easier to drop a detuned S3 engine into the E30 than bother to mess around with the K03 engine.
