I feel that that is not rewind's/gameshark's/cheat code's problem. It's PD'd fault for unnecessarily linking career mode and online. To a 1st order approximation with regard to progression/unlocks, there are two kinds of people. Those who care and those who don't. Obviously, I'm part of the latter. Progression is useless and serves more as a chore than enjoyment in a simulator like GT (IMO). I feel that the simulation of driving is what makes GT, so naturally what I want to do is drive, not play a silly game. Most sims that I have played are pretty much open, barring special modes, etc where limitations make sense.
However, I do not think that my opinion is fact. There are people who find the career mode fun. They should be able to do it if they want. The best answer is to separate online, arcade, and career. Online and arcade would have no unlocks or restrictions. Do whatever. Career would be as has always been. Everyone is satisfied. Unfortunately, PD does not see this or is just unwilling to do this, so it's not likely to happen. This means that you could be considered correct, that bypassing unlocks constitutes cheating. But:
There is more. If GT's online was just one race where any car could be entered, you'd be right because the fastest car would always win. However, GT is more likely to be divided in a number of ways as one would expect a racing to be. You'll have slow races, fast races, and everything in between. The "cheater" has no advantage in this system. Either someone just wants to be able to do all of online ASAP (the "cheater") or they value career mode more (the traditional player). This pretty much eliminates the conflict. If the people rallying for career mode claim it's unfair that the people who don't want to trudge through career mode get things faster, that means they don't really enjoy career mode at all. They just want unlocks, and so they'd really be part of the "cheater" group.
So even in the current model of GT, quick advancement in career can avoid being a form of cheating.
especially not in simulators
To me, progression is something that belongs in a game-game, not a sim-game. Especially when said progression is nothing like real life, which is the case in GT. Career mode is perhaps the least realistic mode of all. It's the most like a game. GT isn't "The Real start life as a college student and rise to F1 champion Simulator" and it's not trying to be. If one believes the limits of mimicking reality must have a limit, and most people do believe this, then they should be able to accept that people will have different ideas of where that limit should be. For me it stops at the race. Outside of a race, reality is irrelevant. I don't care about changing oil (except maybe in an endurance race) buying cars, repairing damage, depositing my paycheck in a bank, scheduling my next dentist appointment, writing a will to simulated family members, etc.
In short, IMO progression is not needed in a game, especially an online one, and especially especially in a simulator. The challege, the fun, the competition of a modern sim is not and cannot be derived from single player. Those things are all found online (IMO).