Do you play with Traction Control on? Because that's the only way I could see someone thinking the two games' physics feel the same. With it off, they are completely different. (Or, rather, as different as they can be while still being based off real cars). I put absurd amounts of time on GT5. Easily in the hundreds of hours, and immediately I noticed a difference in the handling.
The bit about locking out content to force you to buy credits with real money is nonsense. There's not a single thing locked out that would require you to pony up real cash. Cars cost the same amount of money as they did on GT5, and pay outs are similar (though, there aren't the BIG money seasonal events that GT5 had, yet. The Mario Andretti challenge is still worth absurd amounts of credits in it's own right, though.)
I, too, wish that more of the standard cars got turned to premium models, but it's completely understandable that they didn't painstakingly remodel all 1000+ cars in high detail. And if they just got rid of them outright, it would cause more outrage. Everyone would claim the series is going backward by removing cars. They really did the only sensible thing they could do: clean up some of the poorer, more popular models.
I will say that, yes, the AI sucks. But I never really had much issue with rubberbanding when cars were behind me. It's actually kind of funny, they usually fall back with the rest of the pack, and only gain speed when they're ahead of me. But the AI really falls in line with what I expect from the series: I've never really seen it as a game for racing fans, it always seemed more like a game for car enthusiasts. Relying more on pretty graphics and convincing cars, than on breakneck speed and the ultimate challenge. The AI cars, to me, don't seem like they're meant to provide a challenge, they're more like moving obstacles.