well the flamethrowers are there just to put burn status on people, not to outright beat someone into submission.
EDIT: Just gave Dual-Rapier to Izuna and took her for a test drive in Arena, good heavens, it's RIDICULOUSLY hard to aim, and unlike land units, it's hard to follow up even if you do land the hit since you need to lift yourself off first. Gonna give it a few more tries and switching back to Blaster or Mini Bazooka if it doesn't work out.
EDITEDIT: That's it, I give up, it's bad enough that you have to flank all your opponents just to get to those camping artillery units to chop up, then when you do your multi-thrust special you will inevitably get yourself grounded and get pounded by the gazillion reinforcement that comes, and it's hard to aim the rapier from air, so yeah, it's back to Blaster for me.