I'm not really using Atom anymore, but Layout Control has the same functionality this provided plus some other additional stuff.
Sublime Text-like n-column layout shortcuts for atom editor.
Use cmd+alt+[n] (where n is a number) to set the layout to n adjacent vertical panes.
E.g. cmd+alt+3 will create a 3-pane layout.
Good catch. Let us know what about this package looks wrong to you, and we'll investigate right away.