Personally:
Pioneer/Espacio have too much health compared to other cars, considering the cover they give and the very little gap they have at the bottom to negate it. The Fresno is fine because it's tanky, but it's so low profile that it provides almost no cover in most situations.
The 4x4 Vegas, on top of being hard to obtain in a moddable form (bought once per character, account bound for 160 bucks or 7000 to 10000JT grind) has the best acceleration in the game, bar none, a Vaquero can't keep up off the line and that was the fastest accelerating vehicle before it. It's a heavy car. It should not launch like that, otherwise it's fine imo.
Every other "lower-tier" car is fine, if anything, I'd give a small health boost to most of them so they're not just paper and unusable.
The Growl and the Broadwing need their collision model fixed, they get stopped by anything they hit 90% of the time.
The Coywolf could use a small top speed boost.
And finally, one thing to try out: All cars get their max speed capped to 23m/s, but their acceleration is the balancing point. I'd like to see how that plays out.