As the game progresses, here's what I predict needs to happen for a successful team to be flexible.
Controller -> Needs to be able to play Senti as well
Duelist -> Needs to be able to play every single duelist and play orb smokes
Initiator -> Needs to be able to play both Scan and Flash Initiator at a high level
Flex -> Needs to be able to play atleast 1 agent in 3/4 roles to a high level and should be able to play Viper as well
Sentinel -> Honestly they good where they are
Any team built like this should succeed, I am hard pressed to find a reason that they wouldn't succeed.