Hello; With water, gravel, filters, lights, heaters and stuff it couild be an easy 550 pounds. That is a lot of static weight on a dresser that likely was not designed to hold that much.
In addition there will likely be water damage to the dresser. I learned this the hard way when I was a kid and used a dresser for a ten gallon.
The best fix for the dip may be a 3/4 inch sheet of plywood under the tank. You could shim under the plywood.
It may be a good idea to fill up the tank a little at a time and keep an eye for signs of stress.