You're correct in that at one point in CABAL history, FS had the highest spike damage. Not sure whatever happened to that, probably had to do with the Rising Force update where everything was "rebalanced." However, you can't really blame the developers for such changes since a tank class is meant to tank, obviously.

However, where you've gone wrong is claiming that FS has 0 tanking capabilities and are completely useless. First of all, as others have said, it just might be because CABAL has progressed so far now that everyone is in epic gears so you stating that you are unable to tank says a lot about your gears or how you built your character (merit trees). Not sure how easy it is for BL to out damage AoD but there are ways to counter them when they pop AoF such as your charge suppression, or if they're not in combo, evasion pots. BL has immortality for 1x seconds? BLs typically use intuition when they're low on hp, perhaps you could time when you should suppress them with charge. FA has too much evasion? Combo. WI has stun lock and can blink away? Infinite stun, what? You're the only class that retained resist immunity while it got removed from every other class, use it. I'm pretty sure warriors do not have more overall defense than FS do. FB can tank more than FS? Lol, maybe in bm1, highly doubt it otherwise. Yes, they have root but there are so many ways to counter that now...honor 20, holy water pots, panda epaulet, etc. How about we talk about how FBs are nerfed and how completely useless their mana freeze is, even when coupled with Field of Enervation?

In terms of PvE (end game dungeons), FS are probably the most useful since they have Shadow Shield, BM2 Suppression and charge suppression.