The Immolation Arrow does a respectible 1100 points of fire explosion damage then another 750 points of fire damage. This can be a useful skill against those pesky "Physical Immunes." If not for physical immunes, the standard Hit Power Bowzon would be a great build. However, there are many physical immune creatures in version 1.10 of Diablo. So you need to do something to compensate.
In the Fire Bowzon we put zero points into Strafe, pump Multi-Arrow to a conservative 5 (12 or 14 with equipment) and assign the salvaged points into fire skills.
In the Fire Bowzon we do not have the extra points to assign into Penetrate and Valkyrie. This is the cost benefit of developing the fire skills.