I strongly disagree.
We don't know what the reliability will be. The 5.7 has its issues (radiator leak, intake valley leak, air injection pump, starter motor in a difficult location to replace, etc.). We won't know what the reliability will be until years down the road. The assertion that reliability will be worse is an assumption supported by no data. Maybe it won't be as reliable, maybe it will be; we just don't know yet.
As for "best performing" the 5.7 certainly doesn't perform well in terms fuel economy -- fuel economy is horrifically bad. I get 14.5 mpg overall in my 200; 12.5 in the city. That simply isn't acceptable anymore. The 5.7 l in my 2013 200 is rated at 380 hp and 401 lb-ft of torque. The 2.4l hybrid is rated at 326 hp and 465 lb-ft of torque. I suspect that the hybrid will have more torque at lower rpm than the 5.7. The 2.4l hybrid in the 250 should have similar acceleration to the 200 series with the 5.7 while getting 50 to 100% better fuel economy. That sure seems like much better "performance" to me.
What remains to be seen is what the NVH will be like. My guess is that it will be great at lower RPM, but worse at high RPM -- time will tell. I don't know whether that will be a deal breaker. I sure do love the v8 sound of my 5.7l, but I don't like its lack of range or the fact that it uses so much fuel. Yes, I knew how bad it would be when I bought it and I can easily afford the fuel. But it still seems rather profligate to be driving a 12.5 mpg SUV on my commute to work.