[BrickPig]

for the fr-s, didn't subaru and toyota come together to build the engine?

Yes they did, Toyota provided some components, like fuel injection.
2013 Scion FR-S First Drive – Review – Car and Driver

and I was under assumption that the subaru brz shared the engine and there is plenty enough power for the weight.

200 hp @ 7000 rpm, about 2700 lbs, 0-60 in less than 7 seconds. But the real story of this car is chassis balance.
2013 Scion FR-S [w/video] First Drive