I don't recall ever having used mysterious terrain and such. It seems like a waste of time to roll more dice and keep track of what scenery and terrain do through out the game. Our gaming group has even gotten as far as rolling the dice for warlord traits, then picking the table, as more often not, it is of no use.
Sure history is filled with many occurences of this and that, but we are talking about a game, not history. This edition to me seems to be GW over correcting issues from past editions. I would not be surprised if the game swung back into the favour of assaults and vehicles in the future.