Yes the FFB strength changes between cars. The biggest jump in resistance change is when you go from an road car to the X2010, Formula GT car or the Ferrari F1. The most important thing about FFB is that it communicates a lot about what your car is doing in game. The XB1 rumble triggers sound like they are a nice half step between a regular controller and a FFB wheel.
Note: I include the relationship of the transmission to the engine in terms of off-power engine braking, etc, in the general discussion here of "transmissions." I think the term "Powertrain" or "Drivetrain" might work too since that is the entire system that delivers power from the engine to the wheels, but whatever.
Anyone who has driven an automatic car and a manual car instantly notices the difference in how the manual car behaves when you let off the gas in first or second gear compared to automatic. With the AT, you lift and get a nice smooth coast, with the MT, in first or second gear, even at low speeds, you will get a good jolt of engine braking. Supposedly,an F1 car's engine braking
edit: combined with the aero dynamic drag is the equivalent of a high end sports car under full braking load!
In GT games, the same way all of the up shifts are perfectly seamless F1 style shifts no matter what car you are driving, the down shifts behave the same way. Very minimal engine braking happens, super quick down shifts that never disrupt the car, even when you over down shift and smash the rev limiter. The down shifts all generally sound and feel exactly the same across wildly different spec cars.
All of this adds or detracts to the "weight" and total feel of a car. A stock Miata gear box should not feel or sound the same as a 787B. In some "other" sim I play, the lower end RWD cars, like the Miata that don't have the super beefy racing-grade brake rotors and pads, engine braking is a huge part of slowing down. With proper down shifting, you are getting some additional braking at the rear tires (obviously engine braking can only effect the wheels the engine is connected to), which tend to have smaller rear brake rotors. If you go into a corner at 100mph and hold down the clutch or go into neutral, and perfectly threshold brake, and then do the same with proper down shifting, you will substantially shorten your braking distance. If you watch a lot of the "alien" hot laps across several different racing sims, you will notice a lot of them aggressively downshift or dump shift and really squeeze every last bit of the engine braking out of the car since A) you don't care if you blow the engine because it is a game so every .001 of a second is worth the risk and B) not every game models/allows you to blow out your engine or transmission, so go nuts!
I just think that GT is getting the tire and suspension models to a point where they just need a lot of fine tuning for the next installment, (opposed to a massive overhaul like sound fx and AI) and the next area they really should focus on is the feel, behavior, and sound of different transmissions/drivetrains.
For a quick and dirty comparison. Watch the two videos below. Now I know the 787B and the Miata in GT5 and 6 don't sound "identical" but as you will see in the linked videos, they are certainly know where near as different in game as their real life counterparts. Take note of how each car sounds right after an upshift, when the driver is off the gas coasting into a corner, and of course how each car sounds with their respective downshifts and blips.
Miata at Limerock
787B at Le Mans
God I love the way the 787B sounds.
Amen brother.