the OP opened the door there. kubiak was a respected coordinator with no HC experience. he started out his tenure with a 6-10 record and didn't get his first winning season for a couple years after that.
would you say that kubiak is a good HC? better than rivera? based on what exactly? what took him 5-6 years to work on?
They don't have anything in common beyond that. Kubiak inherited a worse roster and a shell shocked QB and still managed to display a measure of competency in his first year. They swept the Jaguars and beat the Colts in a close game, the team who happened to win the superbowl that year.
Also Kubiak started 3-2 his second year, not 1-4.