Rarely ever a problem I have encountered in T4. Not saying that WoF build is the best for all fights in T4, there are a maximum of 2 fights I do not feat for WoF but as a general raiding build the issue of things moving out of range is very rare in T4, if it is a problem it probably more down to poor planning/positioning by the player. Can only think of 1 instance in which WoF is not suitable for T5 and even then it is debatable in my mind depending on tactic. You certainly want it for first and last boss without a doubt.
This isnt an argument against having WoF in your rotation/RoF perk this is an argument against being lazy and not using your insta casts. All my insta casts are kept on cd in my WoF build, so should everybody's
As for finesse and T5 - until I get 8/8 armour pieces (only have 5 atm) and have tested it, I am open to the idea a non WoF build could generate better single target DPS in full T5 gear, but I am not hopeful at first glance of some data a guildie of mine has produced....