if you want 73mm external bearing you're going to have have to go with mtb. good thing it was the best option anyway.

Omniums and most other external bearing cranksets are two piece with the spindle attached to the spider and arm.

110 is not mtb standard but compact road. There are plenty of external options for it.

73 is new mtb standard allowing room for the derailer to mount on the bbshell for frames with now st.