My personal feedback would be mostly around dragon's fury, I've been trying this weapon a lot in pug, and i compared it a lot with stock, as i mainly play pyro in 6's, i can say first it has bugs :
There's some problems of hit detection way more than no damage rockets and shit ( Happened to me around 2-3 times a game)
Then it is not op at all, i would even say underpowered : The fact that you have to aim instead of just spreading flames is very punishing, i've been playing pyro as a substitute of pocket soldier and when it comes to defend your medic, i'd rather just flame the guy than missing my shots and let my medic die. Then, just realize that what makes the pyro that good is also airblast, i'm not saying that it's the most important part to have an impact as pyro but surely it is an ability that allows you to do perfect plays instead of good plays or ok plays, having that nerf airblast may be why i would not use that weapon.
This weapon only becomes interesting when it comes to push a last with full ad for me, but as i'm saying, my pyro's gamestyle is more defensive and protect the medic than ambush and flank things so i could not help you on that in terms of experience, just ask Gazy
then thermal thruster is useless for me, detonator is ,first, too important to have to deal consistent damage and then, why do use a weapon that gives the same things as a deflected rocket jump (ok it can't always happen but you can still do it without this weapon so for me it's useless).
Finally Gas passer can be interesting but only in certain situation, like i imagine thorwing it on the pack while your roamer is sacking for med, must generaly to begin a fight, it can be huge, but at the cost of not having a secondary, which is huge.
To conclude, those 3 weapons can be allowed, certainly not overpowered for me