Vincent's quickness has been a big factor. While I still fear Lowry and his garbage play, it's a different element and one we theoretically should be better equipped to handle. Vincent has been on some real bullshit hitting pull-up threes off the dribble coming around screens and so on. Just makes those defensive recoveries a little bit easier with the much slower player out there instead.
Edit: Marc Davis is a really shitty ref, just objectively terrible at his job, and I assume it's less some kind of bias and more that the Celtics young roster has been A) more likely to respond poorly to what they see as shitty officiating and B) less likely to know how to take advantage of his shitty officiating the way more veteran teams might. They need to keep their cool and play their game and for god's sake throw their heads back!