Looking from the outside I think it's pretty obvious that Cummins is limited tactically as a captain.I agree Cummins needs to drop the captain thing and just put all his mind into bowling.
Cummins is still best bowler in the world and mostly still bowling well.
Smith should be the Australian captain or head.
However, he does seem to have developed a good culture and spirit within the team and during what's a tough tour in terms of the schedule, is a significant plus.
The concern for me would be does the captaincy impact his bowling - others are better placed than me to comment on that.
If he is replaced, I don't think the Aussies should be going back to Smith. Head seems to be well respected as a captain in the Shield and would be the obvious choice I'd think.