Another perspective also on this playoff run - people have quick to hate on the Celtics for having an easy run with so many opposing players out, but something to consider is that this is the playoffs. A lot of it comes down to watching film, studying your opponent, making adjustments, and learning how to take advantage of their weaknesses and minimise their strength.
When a team suddenly loses a key player their talent level might go down, but it also often massively changes the way that team plays. Guys emerge who normally don't get much playing time, teams often share the ball more and play better team ball rather then watching their stars ISO, and in many cases a team can completely change their play style.
If anything the Cavs losing Mitchell mid series and Pacers losing Haliburton mid series probably made things harder for the Celtics, berceuse not you need to re-think all the planning you've done and readjust all over again to the new play style of the team.