They were both boost providers for the Cavs. They lead with different roles and Kyrie's role with the Cavs can never be filled by other powerful players.
Knowing that the Cavs is one of the considered super teams this season after a mega-trade between Irving and some of Boston's superstars plus a former MVP Derrick Rose and Lebron's former tandem in Miami, Dwyane Wade. Their performance is highly criticized especially now that Kyrie and the Boston Celtics are having a great season so far.
Lingering questions everywhere started to sprout due to a very strong winning streak by the Boston Celtics led by Cavs' former guard Kyrie Irving whilst the Cavs, well not so explosive as expected by everyone.
Did Kyrie leave a void that cannot be filled even by multiple superstars?
Without Irving, Cleveland Cavaliers turned out to be a whole lot different team and the addition of too many ace players seemed not to be working that well for their vengeance against the Dubs. If Kyrie left but is then replaced by undeniably good players? Why is it that their potential had dramatically decreased?
Is Kyrie a better player than LeBron James?
Well, we cannot jump to conclusions that far.
LeBron James, without any doubt, is a stronger player than almost anyone in the league. It's just a matter of team chemistry that will explain the current difference between Cavs and Celtics. Maybe Kyrie's style and direction of play are just way more compatible with Boston Celtics. On the other hand, the diverse individual talents possessed by the Cavs still remain asymptotic.