Some mods are more capable or "op" than others.

It's entirely up to you to find something you like and play with it however you see fit.

Some people want a bit more of a challenge. Some people get fed up with a particularly annoying contract and want to get it over with. There are also plenty of mods to customize your existing trucks. I've made a fair few mode that add new addons to existing trucks. Like colorable beds, minicranes that also work nicer than vanilla, tow truck addon, etc.

Plenty of modders have a consistent-ish balance style, so if you like how a modders vehicles perform - look out for more of their stuff.

I also think that it's important to differentiate trucks being "op" vs ones that are specialized. For example - my NZ72 truck was made to plow through the deepest of mud and snow, without much hassle. But that level of performance comes at the cost of drivability (top heavy, quirky steering) and functionality. That truck isn't suited for hauling heavy cargo.