I dont know much about how much current a 6mm draws on 100% throttle, but I do know whenever my brushed crafts feel like they are lacking power it is usually due to a stiff motor shaft from an impact from previous flights..
All motors may be spinning fine when throttling up, but if one is slightly stiff from an impact it will absolutely cause the other motors match and lack in power, just to match up with the weak motor... even a tiny little crash can cause a little bit of "stiffening" lol
if you arm, throttle up to 10%, and disarm right after the props start spinning, you may see a prop stop spinning earlier than the rest, that would be an indicator of the "Stiff" motor..... (This will be completely noticeable with airmode on, a little more difficult to see with airmode off) .. If that is the case, try to carefully take a pair of pliers and pull up on the motorshaft. this should free up the motors a little bit... if you hear a click, then thats a good sign of fixing that motor... if you dont hear a click, then it may not be a stiff motor causing the lack of power, but maybe a weak motor that is nearing the end of its time?
how many flights have you had on that set of motors?