+1 zpromoter
I can't really tell if the dresser is sagging or not, but I do agree that it's not a proper stand. Not to be super technical, but you have a lot of weight there. Since it's all centrally located on the dresser, all of the force is pushing straight down. This in turn will stress the furniture and the tank. If you look at most aquarium stands, the have a board, feet or a flat surface that travels around the entire length of the bottom of the stand. This give more surface area to spread out the weight of the tank and better offer better support. If you look at your dresser, you have 1 leg on each corner and maybe 2 legs in the center. That's 6 individual points of contact and maybe 3 inches each. It's a good possibility that you have all of your service materials and stuff in this dresser as well.
Just my opinion, but I know I wouldn't want 70+ gallons of water in my room or over my clothes one day.
Kenny