The anti-gun bills still need to be passed by the same group, so Deval's influence is mostly symbolic leadership, not stuff he can do directly himself.
Does anyone realy believe Romney or Healey would have vetoed a one gun a month bill, ban on particular types of guns or other bad law? Remember, you're dealing in a state where poltiicians can wear the F rating from GOAL with pride and not even have to waste money on a campaign if they are an incumbent democrat.
The real difference is that any law with positive benefits will probably be vetoed. We recently got 6 year LTCs instead of 4 (but kept the 4x fee increase), free replacement of lost LTCs, and a target gun bill the implementation details of which remain to be worked out. I doubt that any of these would have made it past Deval.