While LeBron James and Kyrie Irving are a dynamic duo for the Cleveland Cavaliers, easily scoring half the points per game between them, the Cavs still need their other players to win games. LeBron's on-court leadership of those other guys is stellar and necessary, making his team's winning offense possible, and making himself look good in the process.
No, I don't think the Cavs lean too heavily on James and Irving for the success of the team. It is true those two are the best players and certainly the most productive (as the statistics bear that out) but the NBA is very competitive and winning teams need a full roster of good players.
It is not that the Cleveland Cavaliers rely too much on two players, it is more that their two All-Stars, Lebron James and Kyrie Irving, are that good where they can usually carry their team. Role players such as Shumpert, Mosgov and Smith, to name a few, contribute serious numbers to the team. Irving and James would not be able to do what they do without the other role players.
Although the Cavs do have two key players which produce a lot of quality plays, each team member is essential to the overall winning or losing of the team. These two key players on the team are relied on the appropriate amount in relation to their abilities to bring forth success for the team and allow all players to contribute what they best can.