Yes, it is correct to say that gravity is the weakest force, because it's the weakest per unit amount of stuff. For instance, if you had two protons near each other the electromagnetic repulsion would be 36 powers of ten stronger than the gravitational force (36 powers of ten is 1 followed by 36 zeros). This is an enormous difference which is why gravity is considered the weakest force.

An important thing to remember about electromagnetism is that it can be attractive or repulsive whereas gravity can just be attractive. In most matter, the attractive and repulsive tendencies are exactly balanced so that you don't even notice the electromagnetic force. But lets say that there were 2 people standing next to each other and they each had 1% more electrons than protons; the repelling force would be so great that it could lift the entire Earth! So essentially the electromagnetic force of a 1% imbalance in charge of a person creates as large a force as a planet does through the gravitational force.

Another important consideration is that since the gravitational force is only attractive, it gets more powerful as objects get larger, but even in these larger objects if the electric charge is balanced out you won't have a stronger electromagnetic force.

So at the scale of planets, stars, galaxies, and black holes, gravity is clearly the most important, but that's only because there is an enormous amount of mass. Basically, the weakest force multiplied by an enormous number (the mass of a star) is very large, but at the same time the fundamental force is considered weak because it is so weak per unit mass.