Has he tried to get it serviced? Just because one phone has problems doesn’t mean all do.
Aside from that, the iPhone 6 was released in 2014, so it’s now a 6-year old phone. Just how long do you expect one to last? How many of your friends have 6-year old Android phones that run perfectly?
My 6s is still working perfectly fine and holding a charge just fine. If my battery goes, I'll likely just get a replacement battery as I'm not interested in the latest and greatest handheld supercomputer that also does phone calls!
I have plenty of friends and coworkers who have had their android phones replaced over the last several years for one reason or another while mine just keeps on going.
Of course, not all phones or all users are the same. I'm feeling pretty lucky that mine has been working perfectly fine for all this time and I hope my luck holds out for a while longer.
Bought my galaxy s3 in 2012 - still works perfectly and only needs to be charged every other day hahahahahaha.