Spoon is clearly Honda biased. Stock for stock, the s2000 has performance advantages over the GT86. 2 Seater vs 2+2 and a stout i4 vs a subaru boxer. Both cars have their pitfalls, but the s2000 is more purpose-built and should do better in most racing scenarios.
I have an FRS, and it's no s2000, but it's a bunch of fun as well. Really wished the car came with a high revving successor to the yamaha tuned toyota engines of yore, but the low center of gravity of the GT86 makes it pretty planted and nimble. I'm glad toyota was able to pull enough of subarus strings to develop the FA20 engine, because n/a subaru motors are BORING. Frankly, I only think it works in this car because of the light weight.