The 480 isn't bottlenecked by the pentium at all, its the same as an i3 6100 in terms of performance.
http://wccftech.com/kaby-lake-pentium-radeon-rx-series-gaming/
Also just because AMD recommends a 500w PSU, doesn't mean that's what it actually draws, its like buying a Honda Civic when technically a lot of people will 'recommend' that you spend heaps of money on unnecessary extras.
That system will only draw about 300w under load, there's heaps of room.
Also what you refer to as a 'better' PSU is very complex, just because a PSU is rated at a certain wattage it doesn't mean it is good, there are many factors such as capacitors, rails, voltage regulation results, stability and OEM.
The PSU I listed is very good and more than enough.