I agree with you mostly on how different the GT3 RSR behaves (and all the 911s). While the pack is expensive and I don't believe we should have been paying what was listed for mostly FM3 cars, it's not the same without Porsche.
I love how much traction the GT3 RSR gets, how quickly it accelerates, and how it just sings to 9K RPM before redline. I definitely had to start weighting the front-end on turn-in to keep from getting understeer and be patient on turn-in not get to too much weight rearward causing lift-off oversteer.
I believe some tuning will alleviate this behavior, but I focused on adjusting my driving style for the car first. These cars drive quite differently (to me) than they did in FM3. I'm happy to have Porsche back in Forza.
I didn't snap any other pictures of the cars I purchased, so sorry for the only showing the one.