Yeah, there will always be matchups that hurt specific teams. A team with huge guards can potentially hurt us (Toronto..), but for the most part, the lack of height has not hurt us. Despite their height, the Celtics had a top 10-12 defense last year and top 5 currently because of their guards and wing players. They aren't perfect, but they are probably the best defensive trio on the perimeter in the NBA by a large extent currently, imo. Their able to get around their shortcomings in a big way. I'm cool with it. IT hasn't hurt us defensively as much as I was worried he would either..
Generally speaking, I actually don't feel like the Celtics are that undersized anymore. A couple years ago when all we had were Sully and Oly, I thought we were very undersized. Now, though? Between Amir, Zeller, Oly, and Sully..even Mickey if he ever plays this year, I'm not really as worried as I was once about being overmatched because of size.