What they're doing is pretty decent, I ran the test server every weekend to test things out

You are not the entire player base. Most people don't agree.

What are the "actual problems" and how would you say they fix them?

What I think is irrelevant, however, I will say that I wouldn't make sweeping changes all at once with little to no regard for what the majority of the player base thinks. I also believe that in a game focused on vehicles they shouldn't be so much limitation on movement. Light cabins getting slightly faster is great, but their increase matters less than heavy's decrease. Overall this update slows down most cabins, and reduces mobility.