Neutral.
I agree that there are two points of this rune that are kinda broken.
- It prolongs duration. And by quite a lot for every kill.
- It prolongs duration even when you use different weapon and kill enemies.
Without recharge this rune only gives you stealth for survivability and sort of a damage boost due to using stealth attack. Which sometimes breaks and does not work (there are cases when enemies are immune to stealth attacks for some reason).
Without stealth attack, it will only give you invisibility.
Mind you that almost all bosses are already immune to stealth attack.
[Only bosses that you can stealth attack are Bannerets, Castellans and Gruul Seeker Ruthos. Not sure about Knell Knight]
And don't forget that alternate rune gives you block ignore and +100% to damage on any attack. If anything in terms of damage, fire rune gives you more on average, as stealth attacks only come to parity.
And The Flintsmoke is a rune from Cogah mode, which is increased difficulty for increased reward quality.
Newly added bow The Torrent rune can currently burst Banneret down in less than one second for some reason. AND it seems to ignore enemy armour at that? [For context i think that The Torrent definitely needs to be adjusted]
Newly added magick The Hollowing rune allows you to quite literally explode enemy packs on single enemy death.
Looking at these two, stealth and freebie stealth attacks for 25 seconds (duration of basically all runes) don't look too broken.
Main issue with The Flintsmoke rune is that adjusting it is hard.
- Restricting invisibility to single strike is stupid as it will make rune basically unusable.
- Restricting effect by limiting stealth attack during this particular invisibility is better.
- But i think that worst offender of this rune is specifically prolongation of an effect and not an effect itself. Disable it, and rune becomes much more in line.