[I'm not the AC, just to avoid confusion]

To sum it up, it doesn't matter whether something is subatomic or not, gravity acts the same. A chunk of matter consists of of subatomic particles after all, therefore all gravity it experiences is through the particles it consists of.

Another thing is that there are quite obvious examples of gravity playing an important part on non-solid matter: gas clouds and suns. Suns are created from collapsing clouds of hydrogen, helium and some heavier elements. Almost all of that exists as atomic or small molecular particles, not as even sand grain sized chunks.

Of course EM has a big influence on matter, but consider this: All clouds, once collapsing will continue to do so until radiation pressure stops them. That radiation is from nuclear fusion in stars. In our sun, gravity is strong enough to contract one mighty amount of matter strong enough to create 15 million Kelvin in its center to keep running a fusion core that converts millions of tons of mass into energy. There's no solid chunks of anything involved.

Yet another way to put it: Gravity is global; it only adds up. The other forces may be stronger, but they don't reach as far or cancel themselves out locally. So gravity is the only significant force on the galactic level.