It's not even near realistic/believable, V's system is more realistic overall.
Please explain how its more realistic?
IV's problem was that the physics were exaggerated. Sports cars handled like 1960s Sedans when they in fact are more likely to handle like V's cars. Mid-tier cars could not accelerate to a certain point. Things like that that I think are more big picture than the small picture from V's mechanics.
V's cars had more realistic responsiveness depending on the car. A sports car will feel more responsive than a sedan. My car is fairly old. It's an early 90s sedan. My dad's car (well, the one he uses the most now) is a lot newer, it's a mid 2000s sports truck. Even with it being a lot larger than my car, the responsiveness is a lot more apparent: my car takes more effort to turn than does his. I can only imagine how more responsive a top-of-the-line modern-day sports car is compared to mine. V represents this albeit pretty exaggerated.
V also has a little bit more realistic speed physics: low/mid-tier cars can reach top speeds over time, while in IV, they couldn't. Not only that, the turns at high speeds in IV were completely unrealistic. Sure, your car's gonna flip the f*ck over if you're going 160 mph and steer the wheel immediately, but as someone who spends most of his driving time at 65 mph+, I can tell you that cars aren't gonna flip over just by slightly tilting at higher speeds. Hell, I've driven at ~120mph (I was a naughty boy), and the steering was fine as long as I kept the steering steady and didn't make any sudden movements. In IV, at the slightest tilt at high speeds, your car would flip sh*t.
As far as offroad vs sportscars, I agree there for the most part, but I will say that generally, with offroad cars, I can climb mountains at a slow pace compared to having to hold the pedal to the floor with sports cars. Also, you can't really use this as a one-up on IV since there wasn't much countryside to test this out in it.
And a lot of your bulletpoints are opinions.