Fangs sab role will have everything but poison later on, I say keep Fang cause she is also the best commando until Sazh becomes god (he pretty much does
, skill wise, not story wise, I don't wanna spoil that).
Hope is bad? What have you upgraded with him? Peanut butter?
He got the best magic stat, all magics for ravager (exception for the -strikes attacks), synergist only missing vigilance, no annoying screamy sounds when he attacks.
Only bad thing he got the worst HP of all, I think I can change him to Lightning so my team will be Sazh/Fang/Lightning.
Slow is a savior, Vanille's early Deprotect and Deshell is good but Fang get's both later on.
You'll need a synergist on your team if your on chapter 11+. Two saboteurs can be good but not in the long run.
A sentinel is also great to use for a painfree healing.