Since this IS a blowtorch, couldnt it be a wrench?
Instead of 25 metal at a time, it rapidly does +1.
The rate would be the same as a lvl 3 dispenser healing someone.
This would probrably decrease the building speed as well.
It lighting on fire is ok, because like the sniper, yet has a spy defender, because spies hate fire
Since its not a wrench, it will of course have less range.

PS: A cool taunt kill for this would be you applying oil to the end then a massive flame comes out.