Well seems like the kanji 並 means "rival" "equal to" "rank" and seems like it indicates in this case two men togheter that are on the same level of importance
and
肩を並べる means also "to be on a par with" with the same Kanji 並
Now I'm not an expert in japanese but it's not like
肩を並べる can be translated only as "To stand togheter". With the context of the chapter and how Oimo tell a story about Gaban and his strenght maybe it could be used the "to be on a par with" translation.
But I'm no expert, I repeat.