Very true but you can't target designate/lock on to all the vehicles, if you have a good amount of jav. users, tanks and boats won't even make it to the beach
The good thing about those place down items is that they are hard to destroy especially with normal gun fire, if you place them in such a way on the hill so that it isn't completely exposed, the enemy team will have a very hard time destroying it.
Thankfully the majority of players don't seem to know that the MAV can destroy soflams, tugs, stationary mavs