I think companion are differentiated into two groups, front and rear types.

Mercenary-melee is a front-type companion, Mercenary-archer and Indiana Jones are rear-type companions.

There are some companions comes in two person, or able to summon creatures to aid in battle.

Indiana Jones is the type of companion that deals melee, area of effect, stamina damage (Yellow damage), pretty dangerous if aggro'd by accident, since Lona is pretty low on stamina. Since some enemies have significantly lower Stamina level, Indiana Jones is very capable at weeding them out with its AoE whip attacks.

Edit: Correction and updates