1 on their own is not up to the role but two together works better (Holt & Jacko or Holt & Moro). As I said though, if something else is tried out and is seen to be working I will be happy enough.
I fully understand the flexibility of the 4-5-1 and accept it can work very well if played right but it does need the right players and those players need to be well disciplined to get back when needed (as per my overwhelmed in midfield statement earlier). We have already seen countless times that if our midfield are caught out, our back line takes the hit too. If that can be addressed then yes it can work but we are yet to see it work well on a consistent basis because the manager(s) keep trying "other" things, so to that end I cannot be convinced that it IS THE THING to do but accept IT IS THE THING to try out for a run of games.