Lower HP means you are competing with a lower class of cars in terms of power. Giving it an advantage in the market segment to justify the higher price. Or make it look like an engineering marvel.
Keep in mind that turbo charging is the easiest way to make HP, so claiming to make 550 from a 3.8 engine is not as jaw dropping as having ~470 hp and beating anything up to 650. Thus "proving" its advance chassis design, drivetrain, and engine tuning.
It's more about brand polishing than it's about cars
This is a product to make ppl that can't afford a GT-R believe they are getting similar treatment in the POS lower lineup.