I mean really, if BTF hurt enemies, it might justify itself better. But right now the only thing it is actually good at accomplishing is letting the Sacrier push themselves to or below 50%. What Delaz demonstrated is that its supposed primary purpose (boosting fire damage) doesn't work.
(EDIT: it works in the very literal sense in that the bonus is applied. Just not in any sense that anyone cares about, because the AP is better spent on other spells)
81 x 1.3 - 81 = 24 - Blood rush
115 x 1.3 - 115 = 34.5 - Burning Blood to 115 x 1.4 x 1.3 - 161 = 48.3
108 x 1.3 - 108 = 32.4 - Cage of Blood
177.5 x 1.3 - 177.5 = 53 Punshiment at 50% hp(Which is when it's supposed to be competitive)
With the exception of Blood rush which I find it hard to find use other than " I need flaming while tanking, and blood rush happens to be the cheapest option" BTF is great. Majority of Fire spells are worse than it after first use, Which is IMO a larger problem then BTF.
The only diminishing return was in Blood rush. BTF deals some bit more than 2 AP worth of HP, which is why I said it may take too much HP. But then again, it's intended purpose was to reduce HP for the Sacrier with benefit.
Honestly, sometimes I think the majority of Sacrier problems lies with everyone wants to do everything. Mechanically their Damage dealing is flawed and has lower potential than may be theoretically possible. HOWEVER, Positioning and Tanking are very powerful for Sacrier, In theory, Assault +Motionsickness is enough to consistently out damage Cra. In practice, you don't get backstab so it's actually less than actually possible. Zerous did a pretty decent job, I expected him to gut the class but he left a lot of mechanics that I expected to get torn apart with their initial effect(I was almost certain Transport was going to get gutted, but he just nerfed it's usefulness while buffing it by reducing it's AP cost). I'm almost certain Sacrier suffers from the same amount of issues Iop does. Which leads me to believe they're not as bad as everyone acts like they are, but definitely could use tweaks. Like every class ever.
But, Delaz's post had too many glaring flaws and issues.
"Nerfing it's usefulness while buffing it by reducing AP cost", have you actually played sacrier?
Using mobility passive to get that reduce AP takes away -100 resist, try being tanky and mobile with a passive taking away 100 resist and let me know how well your tanking goes at say places like any moon island dungeon.