This was my take as well, but
Pink Eye has pointed out there are a lot of strong Faythe builds.
I think I have the most builds submitted for her at this point. At least in that steam build thread. Also tried every single weapon class and as many feat combinations as I can on her. Faythe's main strengths are two fold: 1) Her Assassin Feat that allows her to be built in a variety of ways (She gets free +10 innate penetration, +5 CS, and Extra melee damage which makes for low Str) 2) Starting tags - her starting four at the start allows you to tag on defensive skill, or both if you want, i.e armor handling + evasion; and one combat skill. While also having enough to tag another civic skill. The reason why that's significant is because tagging a skill immediately bumps it up by two levels. This means she's combat ready from the start. In the past I had to really maximize what encounters I did in order to get Faythe to "grind" her combat skills on easy fights. Nowadays this isn't really that necessary.
In regards to that other point of her being flexible I'd like to share a couple of builds I did on her. Now this isn't meant for you copy pasta, or me showing off, just trying to showcase what you can pull off on her.
Recently I did a "Reaction" themed build on her:
That was pretty fun. She managed to get 100+ Reaction Chance with a nice Revolver from Habitat and Braxton's HUD which grants reaction bonus too. Could have taken it even further with Caption feat which would have granted another +20 bonus.
Another was the Rifle/Initiative:
Between Heavy Armor Faythe and Initiative Rifle - this one is my favorite because of how much AP she's able to get at start with Fast Draw then quickly triggers Second Wind by one tapping enemies. Comes in clutch in big fights like the double pysker encounter at Hydro.
Ooh! This is another one of my favorite. The Bloodlust SMG Faythe
I made a mistake there. I picked Master Blaster feat instead of Sharpshooter though. Ended up hurting a bit though, not too much though. Couple of good SMGs with innate penetration.
Lastly there's Basher Faythe too. Synergies so nicely with her Assassin feat: