Seems kinda like you're making my point for me.
More over, a "young" male who likes sporty cars and goes out to buy a brand-new v6 mustang isn't all that different from the others. In fact, I'd say that's pretty far from the type of person I believe would notice driving dynamics in general.
Fact of the matter is... If I was the type willing to spend 25k on a mustang purely for a "sporty" car, I certainly wouldn't buy a 2013 v6. I mean... Is it really a stretch for you to see a sports car oriented young man would probably go buy an 8cyl. mustang from 2 years earlier?
My first point was that if you're a young sports car enthusiast in America and want to buy a brand new, sporty car, it would make more sense to buy a V6 Mustang over the Scion in the US. The Mustang would offer more power (by about a 100hp more), quicker 0-60, and similar handling ability. The Genesis Coupe is another option too since it offers similar to better performance than the Mustang, however it's more expensive.
My second point was, most sport cars enthusiast who are young typically don't buy new cars, so it's a limited market Scion is trying to cater to since they are a brand solely devoted to young people. I don't really see where this Scion fits in at all in that limited market since there are better options out there.
I fail to see how buying a V6 Mustang makes you not care about driving dynamics. Sure you could buy a couple year old Mustang GT, but that's looking at used cars which has no bearing on my example with new cars. It's not a stretch for me at all to see why someone would rather get a used GT over a V6, but like I said it doesn't fit within my example.
So to sum it up: If you are young enthusiast and want something new, sporty and RWD for $23,000 there are better options than the Scion. However, since most young enthusiast want something used, sport and RWD for less money the market for the FR-S is limited. Withing that limited market I believe it will have a hard time going up against better cars.
I just don't see enthusiasts around the world saying...
Man I need a car at 25k and Im equally considering a Brz and a Mustang v6.
I haven't said anything about the rest of the world, my point is strictly for America. I don't know enough about what's offered elsewhere.
Again, I'd say it's more like...
I'm going to get a mustang or (insert another other american muscle car)
or
I'm going to get a Brz or a genesis coupe.
If you were a smart car buyer looking for something new, sporty, RWD and around $23,000 I don't see why you wouldn't consider the Mustang, Genesis, FR-S and a Miata. The Mustang is more of a sports car now than it used to be, it's no longer there for quarter miles. If you drove all 4 vehicles I would wager that you'd end up not buying the FR-S in favour of something different barring you aren't a huge Toyota fanboy.