Dominion is the most power weapon laden gametype in halo 4.
The 3 bases constantly spawn random ordnance every 30 seconds and most of the time they are rocket launchers, sniper rifles, and other power weapons. The map seems to have a factor in what spawns too, if your on exile, expect a massive amount of rocket launchers and saws and sniper rifles.
If your on meltdown, expect nothing but Promethean ordnance.
As for vehicles being weak, they do suck in halo 4, but you can double their durability but using wheel-man combined with the explosive perk. I've survived things in the scorpion tank with that combo that seems insane.