Steady Shot Rank 1 110 Mana
Multi-Shot Rank 6 275 Mana
Bringing the average damage from your WWS
Steady avg 952 -> 8,654 damage per mana
Multi avg 1101 -> 4,0036 damage per mana
As others have already pointed out .. it's a matter of efficiency and depends by situations. A 3 minute fight doesnt sound to me to be a great example as you may bear your mind most on longer encounters imho.
Reading posted informations I may say that Steady Shot is double efficient than multi for a Beast Master on a single target encounter. Period.