Yes, your buddy is right. The less restriction you have at the exhaust end, the more efficient your engine can breathe. Same with air intake at the front end.
There is also some merit in having a tuned exhaust for certain types of racing. This is another story althogether and to get the best tuned exhaust for certain applications, you really need to dyno the engine. I used to race GoKarts (2 stroke engines) and we ran with "canned" pipe coming out back of engine. Manuafacturers would sell different design, length pipes for short sprint races or longer track enduro type races. The process is no different than changing rear axle gear ratios depending on the type of track your running.

You can imagine running a marathon race or even a sprint race and you have to wear a mask.
When you breathe in and out, your body has to work harder because of the restriction.

I was surprised when I seen the Borla system. It looks something of a Boilermans worse nightmare.
However, I think they were trying to maintain factory low-end torque specs by keeping some backpressure and of course they likely didn't want to create a system with too loud a sound. The "dual" designed system would have been a lot more expensive for them to meet their objective.
I think they are being somewhat cautious because they have to mass produce these to a mass market. However, nothing can beat a custom system designed to meet objectives of one individual.