I've seen much better C's teams get destroyed easier.
Watching a much better team get killed is a different kind of painful. In that case, you know they're capable of competing, but they don't.
The Celtics didn't play their best game today, but I think they played a lot closer to their best than the Cavs did. They're just nowhere close to being ready to hang with a contender, and it shows.
All of that would be fine if they all kinds of potential and just needed time to grow. This isn't the 2010 Thunder.