Dirtbike ignition system: power consumption
Your power estimates are way too high like you say.You should measure or google or get the inductance of the coil .Once you have  L then in your formula it goes .Its now an LR circuit where the current builds slowly starting from zero and limiting out given dwell time at your DCR value .With sensible parameters the coil finishing current wont get that high so your average coil current which is your current consumption on inductive ignition system will be much lower than your estimate .Realy your estimate assumes that L is zero  or can be neglected which is not true here .