Should I max out every vehicle for progression?

It's up to you. I spade vehicles before I jump to next one, but it just me and my way of playing WT.
IMHO if you are not a big fan of specific vehicle, there is no reason to force yourself and spade it, especially if you want to get into some specific machine that lay a bit further in tech tree.
Just remember to have some decent lineup for your BR. You will get much more from battles if you use more than 1 vehicle - more time in battle, more activity = higher rewards.