Combat Engineer progession not benefiting from using vehicles

It looks like when you pick the vehicle trait for engineer you don't really get any progress from the fact you use a vehicle which is kinda odd. Almost more beneficial to first boost the trait on a different class that makes it much easier, than just swap later, it's a bit odd.

It sometimes takes for ever to get progress even if you top the scoreboard, while it feels with some other classes you just get it for free.