For just 8k more, you're getting a phone that's better in almost all imaginable aspects, apart from pixel density of the display and build material.
5.4" vs. 6.5" display. 2,800mAh vs. 5,000mAh battery. dual vs. quad cameras. used vs. brand new with warranty. Android 9.0 vs. Android 7.1 OS.
List goes on and on...

The G5 will be a temporary phone and in an year or two he'll start experience battery drain issues IF he's lucky, whereas the R5 will last him a long LONG time.
You get what you pay for, my dear friend!
