Your friend is nuts! But then I would say that. Listen there is no comparison. If you want an amazing gaming experience and a system thats relative for 4-5 years go all out.
If you wanna have a poor gaming experience, wonder why stuff keeps stuttering and your gameplay isn't as you'd expect, then stick an i5 or i7 in there with a GTX1080.
Now with all of that said, it depends on what I5/I7 you're talking about!!
Spending big bucks on a system means it will last, and still play games in 4-5 years. But nonetheless, new hardware comes out all the time, and it's only a few months typically after purchase, and then the next better chips comes out. PC systems are never really obsolete (unless they die), but in comparison to the next 'one' it will be slower. and so on.
Take my own system for example. 2 years ago my Ryzen 1600x was a great midrange CPU with pretty amazing performance (for what it was). now the Ryzen 2600x is already out (and is about 10$ faster) and by the end of the year the Ryzen 3600x will be out, and it will be stellar! This happens. That the hardware world we live in. Nothing is future proof. The more you spend at the beginning, the less you have to spend down the line. But that's the fun part for me. Upgrading bits as I go along.