No one is questioning the fact that the eutectic alloys arent strong. Hell, they are great pistons really. the problem is, that they are brittle- very brittle. they hold their "shape" better than forged, where a forged piston will deflect and then return when stressed. The eutectic alloy will not deflect- to a point, but then it CRACKS when it does. Not good if you have any detonation which is the equivalent of hitting the piston with a hammer.
I have seen more than one eutectic piston literally crack to peices just from trying to disassemble it off of the rod. The pin, press fit in gen 2/3, "pops" when it comes loose from the rod in a hydraulic press, and that harmonic alone while pressing against the piston with the press at times can shatter the pistons.
The biggest problem however comes from its design, not just its material. The "cast" pistons have very high ring placement, making the ring lands and rings themselves very easy targets for detonation damage.