It does seem (in theory) that smaller boards, with new melta and eradicators rules, will lead to vehicles dying like flies. Perhaps all vehicles need a duty eternal/-1damage rule?
Vehicles got a an offensive buff in 9th in that they can all now move and fire at full effect.Unfortunately that does nothing for their survivability (although I suppose killing your enemy is a pretty good way to survive ).
I think screening vehicles is going to be important, even for an army like Marines, as will the choice of vehicle. Many Marine vehicles are now T8 so meltas only wound on a 4+. Use screening to stop Eradicators getting within 12". Even consider using a Librarian with Psychic Fortress for a bubble of 5++.
Eliminators are basically a one-shot unit because coming on close to the enemy for a small squad is not likely to end well. A regular squad is only 9 wounds, even if they are at T5. If they are close to you, tag them in combat and you don't have to worry about them (unless they are pesky Ultramarines ).
Vehicles need support in 9th. They are more powerful than in 8th but there are bigger guns out there so you need a combined arms approach. You cannot leave them unprotected or specialist tank hunters will have a field day. The other option of course is to go infantry-spam and deny those melta rifles any high value targets.