It's not that amd is for gaming or intel is for gaming. They're both cpu's with different architectures, means of achieving the same goal. For the past several years intel has had the upper hand in just about every benchmark and it's not a slam against amd, it's just the way it is. Benchmark after benchmark keep turning up the same results.
Cpu's are priced pretty evenly if you ignore core count and core speed. Core speed means nothing comparing one platform to the other anyway. You'll notice an i3 and fx 63xx are similar in price and their performance is pretty even across the board. In a few tasks the fx will have a slight edge, in a few tasks the i3 will. An fx 8xxx tends to perform similar to an i3 in some situations and closer to an i5 in others, usually falling somewhere in between. It's priced higher than an i3 and less than an i5. Intel cpu's don't cost more compared to relative performance, they cost more because they perform better.
Does it mean intel is the absolute only choice? Of course not. But you tend to get what you pay for much like most other things. I own a kitchenaid or some random brand blender and it costs around $40. Is a $600 vitamix blender better, larger capacity, better built, better performing? Absolutely. For my needs the standard blender I got from the local store was 'good enough'. It still blends ice and things for the occasions I need it.
Will amd always be behind intel? Maybe or maybe not, it's been the other way around in the past and can go that way again. Zen has yet to come out so can't say for sure until it does. As others have said it depends on the tasks, the rest of the system, the software. There are a couple of games out there that saw a bigger fps increase from win7 to win8.1 than they get from changing from an i5 to an i7.
When it comes to a friend making statements it would help to know in what tasks the fx 8350 was better. By how much, what measurement. That's why benchmarks exist, sometimes people 'feel' a certain way but the only reliable way to quantify anything is via a benchmark. Compare fps to fps with all else being equal, same data drive, same speed and amount of ram and so on. Or compare a task such as encoding a specific video from one format to another and timing it. 65mph 'feels' faster on a motorcycle than it does in a semi truck but in reality it's the same 65mph.
An fx 8350 is $45 more than an i3 6100. If your friend had spent another $45 they could've gotten an i5 which most likely would have been faster in just about every task. It's not that amd performs better and it's cheaper, you pit a more expensive cpu against a less expensive one I would hope it performed at least a little better. It's apples and oranges. I could say the exact same by saying I got an i7 and it was faster than an fx 6300 so people with amd don't know what they're talking about. For 3x the price I would hope so.
The typical thought is that more cores means better performance in heavily threaded scenarios or better performance in multitasking. Not always true.
http://www.bit-tech.net/hardware/2014/09/03/intel-core-i7-5930k-and-core-i7-5820k-revie/5
Here's the total aggregate results from a variety of tests, real world apps, photo programs, video encoding, compression software etc. Some single threaded some multithreaded. The 4th gen i5 and i7 both came out ahead of the fx 8350. The fx 8350 overall came out behind the i5 yet ahead of the i3 and the i3 was almost dead even with the fx 6xxx which follows their pricing structure in the same exact order.
http://www.tomshardware.com/charts/cpu-charts-2015/-36-Total-Time,3728.html