The trouble was that the 20th century physics community was never happy and satisfied with that realization. They saw subatomic particles and jumped to a false conclusion that atoms were not the last cut. Their false conclusion is based on the idea that an electron or proton or neutron have independent existence and that the separation by an arbitrary distance meant that the atom was not the last cut. But they are wrong. Just because you have an electron separated from a proton by light years does not mean it is not an hydrogen atom.
Atoms are the last cut.
And the particle zoo physics is a wastrel disappointment down pseudo lane. The Uncertainty Principle says as much. Fermilab, near Chicago, that quarks just might be made up of something even smaller. . . The protons and antiprotons contain quarks, along with particles called gluons that bind the quarks together. Occasionally, a quark or gluon from a proton collides head-on with a quark or gluon from an antiproton.