Again, since some people don't read. GT5 is a game you can play your own way, they don't force much on you early on. You are giving criteria for a race and it's up to you to choose how you want to race, stock, fully modded or under powered. Instead of "you must use x car, with y hp and z weight". Every game I have played has done that to death. Game feels like 2005? Really? How so? Since back then they forced you to drive with rules laid out and you couldn't do a damn thing about it, how is giving you the option to choose how you want to have your enjoyment a bad thing? Some people don't know how good something is until it's taken away.
The PI system in FM3 was broken due to 4wd swaps, which for all cases makes no sense for most cars, 200+lbs weight increase results in nearly 50 point PI drop, then you tune back up to top PI and you'll smack around most cars in your class. Hence the leaderboards littered with AWD modded cars, you may find one or two rear wheel driven cars, but S class forget about it.
The PP system in Prologue would be good to add to online, but wouldn't be necessary in single player, since you are given freedom to rule your self, what you don't have such ability do you? You need to be told what to do, it's nothing to be ashamed of it's built into all humans the need to be led by someone greater than ourselves. Without it there would be anarchy, but in singleplayer there isn't anything wrong with freedom to make decisions. Try driving a comparable car to the competition if you dare and stop complaining that the game doesn't force you to play by arbitrary rules that border on being the same crap from 20 years ago.
Freedom of choice is becoming something that little actually understand and even less embrace...If you want a rule laden race come online someone will gladly setup a room with strict rules and restrictions and you will get your kicks there. Some of the races in single player were tough with a stock vehicle, because incidentally stock vehicles all perform the same and when the AI decides to drive perfectly, you won't win anyway you slice it.
To the guy above, you must not be paying attention to the usual suspects addition to GT5, before you enter a race you can check what cars you will most likely be up against, so this whole thing about needing PP in single player is made up, as you are given Hp, and weight as well as the name of the car.